The Old Norse reckoned that there were three races of Gods: the Aesir, the Vanir, and the Jotnar. The Aesir are those beings most often referred to in the ancient literature simply as "the Gods," in fact the word "As" means "God." They are the Gods of human society, representing things such as leadership, craft, justice, etc. The Vanir are more closely connected to the earth and represent the fecundity of the land and sea, and the natural forces which help mankind. Once there was a great war between the Aesir and the Vanir, but this was eventually settled when it was determined that neither side could win, and Frey, Freya, and Njord came to live with the Aesir to seal the peace. The Jotnar are a third race of Gods and at constant war with the Aesir, but there is not and never will be peace in this battle. The Jotnar are never called Gods, but rather referred to as giants. They represent the natural forces of chaos and destruction as the Aesir represent forces of order and society. Just as fire and ice mix to form the world, this creative interaction of chaos and order maintains the balance of the world. In the end the two sides will meet in the great battle of Ragnarok and the world will be destroyed, only to be reborn.
The Norse notion of the Gods was very much involved with tribalism. The Aesir are the Gods of the tribe or clan. The Vanir are those Gods who are allied with the clan, but who are not part of it. The Jotnar or Giants are the "outlanders" or more simply everyone else.
The Norse Gods were not held to be all powerful or immortal. Their youth was maintained very precariously by the magickal apples of the Goddess Idunna. More importantly at the end of the world a good number of the Gods will die in battle. The Northern view of the world was a practical one with little assurance for the future and little perfection and the Gods are no exception.
It is very important to understand that the Gods are real and living beings. They are not mere personifications of natural forces, nor are they Jungian archetypes that dwell only in our minds--although Jung's work may be helpful in understanding their nature as living beings. Those divinities who we call "Gods" (i.e., the Aesir and Vanir) are also "personal deities" who take an active interest in the affairs of mankind, and seek relationships with their followers. This is important to remember when we perform ceremonies or pray to the Gods. They aren't magical symbols to be manipulated, nor is our religion some type of giant cosmic vending machine where sacrifices are inserted and blessings come out. The Gods are living beings and offer us benefits because we are their friends and companions. They should always be treated with respect.
The three most important Gods were held to be Odin, Thor, and Frey. These were the deities whose statues stood at the altar of the temple at Upsalla. They are considered the most important because of what they represent. Mythologer Georges Dumezil has linked these three deities with the three classes of Indo-European culture: the Kings, the Warriors, and the Farmers. Although the fit is not an exact one, it is probably true that these three deities most concretely symbolized the various aspects of Norse life and culture and most people would have found a God who represented their life-experience in one of these three deities.
Odin is the Allfather, remembered today best as a God of war and of the berserk rage of the Vikings. However, he has other aspects which are just as strong or stronger. In the Eddas, he is the leader of the Gods, but this is a position which most of the Germanic peoples attributed to Tyr. It's likely that Odin only became ruler during the Viking Age, when a God of wile rather than strict justice was more necessary. Being the Allfather, his original position of leadership was probably familial rather than legislative. Most importantly he is a God of transcendent wisdom and in relation to that a God of magick. He is the God of the Runes, the magical alphabet which holds the mysteries of the universe within it. In most of the non-Viking countries, Odin's warrior aspect was played down. In England, where he is known as Woden, he is a gray cloaked wanderer (the inspiration for Tolkien's Gandalf) who travels the country, usually alone, surveying his land. Here again we see him in the position of a father figure, a warder of the land but not necessarily a King. Odin is also a God of the dead. It is said that half of the slain in battles go to him to prepare for the Ragnarok. (The remaining half go to Freya.) He also has associations with the dead as a practitioner of Seidhr, a form of shamanic magick which he learned from Freya and used on various occasions to travel to Hel and seek the knowledge of those who have passed from this world. It's difficult to classify Odin simply because he was such a popular God during the last stages of Norse Paganism and thus absorbed many traits of other Gods.
Thor is probably the best known of the Norse Gods. He is a simple God, the patron of farmers and other folk who are "wise, but not too wise" as the Eddas advise us to be. Thor is best known for wandering the world in search of adventure; usually found in the form of giants or other monsters to kill. He possesses tremendous strength and the hammer Mjolnir, which was made for him by the Dwarfs. Mjolnir is considered to be the Gods' greatest treasure because it is sure protection from the forces of the Jotnar. Using Mjolnir, Thor is a warrior figure, but he is less a professional warrior than a common man called upon to defend his land. He loves battle not for itself as do the berserkers of Odin, nor does he have a strong code of honor such as that of Tyr--in fact he breaks with honor and kills giants whether they have the protection of "hospitality" or not. Thor is associated with thunder and lightning, but it's important to note that he is not the God of destructive storms, thunder and lightning were associated with the summer storms that brought swift crop growth. Thor is nature as a benefit to man. The Jotnar are held to be the source of the destruction found in nature. Thor was the God of "everyman." He was simple in purpose, strong, and free. He was most beloved of the freemen farmers who populated the Germanic lands.
Frey is a God of peace and fertility. If Thor is the God of the farmer, then Frey is the God of the crops themselves. He is a God of the Vanir, but lives with the Aesir to secure their treaty with the Vanir. His symbol is the priapus and his blessings were sought at planting and other important agricultural festivals. The word "frey" means "Lord" and it's unsure if this is the Gods name or his title. He is also known as Ing or Ingvi, so some have speculated his title is properly Frey Ingvi--Lord Ingvi. We do not known a great deal more about Frey as few myths have survived which give us any insight into his character. As much as he is a God of fertility, he is also a God of peace and Ing was said to have brought a Golden Age of peace and prosperity to old Denmark. Horses are held to be sacred to Frey, probably because of fertility connections.
In general we know much less about how our ancestors worshipped the Goddesses than the Gods. Later Norse culture was very bound up with the vikings and it is likely that the Goddesses were deemphasized at this point. More importantly, virtually all the mythology we have today was recorded during the Christian period and Christian culture had little respect for women.
Freya is the most important of the Goddesses or at least that Goddess about which we known the most. She is the sister of Frey and along with him was sent to live with the Aesir in order to seal a peace agreement. Freya is a Goddess with several distinct sides. First, she is the Goddess of love and beauty and second a Goddess of war who shares the battle-slain with Odin. She was also a sorceress who practiced the shamanic magick known as Seidhr, which she taught to Odin. Freya is the Goddess most often invoked by independent women. While she is a Goddess of beauty, she is not dependent on men as is the stereotype of so many love Goddesses, but is strong and fiercely independent. She is also known as the Great Dis and probably has connections to the family spirits known as the Disir. In many ways she is like Odin in that she is a Goddess of many functions which are not always obviously related. In modern Asatru, many groups have placed Freya alongside Odin and Thor on the altar, in place of her twin brother Frey.
Frigg is a most misunderstood Goddess. She is the wife of Odin and many people are too willing to let her be known simply as that. However, the old Norse had a much different idea of the place of women and of marriage in general. While marriages for love were certainly known, marriage was also a business and social arrangement and there were important duties for a wife. These were symbolized by a set of keys which hung at the belt of all "goodwives." This symbolized that the home was under the control of the woman of the house, who was equal to her husband. Today we think these duties as very minor, but a thousand years ago they were far from trivial. Up until this century most of Europe lived in extended families. A house, especially a hall of a warrior, was not a small building with a nuclear family, but an entire settlement with outbuildings, servants, slaves, and an entire clan. The wife of the house was in charge of stores and trading with other clans. It was she that saw to the upkeep of the farm, the balancing of the books, and even to the farming itself if her husband was away trading or making war. It was as much a job of managing a business as it was being a "wife." For these reasons Frigg is still very important and can easily be invoked beyond the home. She would, for example, be a natural patron for someone who owned a business. Frigg also shares a lot of characteristics with her husband. She is the only other God who is allowed to sit in Odin's seat from which can be seen all that goes on in the nine worlds. It is said that she knows the future, but remains silent, which is entirely in keeping with the way women of the time exercised their power: namely indirectly. While in a better world this might not be necessary, it is still an important tool for women who must exist in a world where men are sometimes threatened by them. While Freya is a Goddess who acts independent of "traditional" roles, Frigg is a Goddess who works within those roles, but still maintains her power and independence.
There are of course many other Gods and Goddesses. Some of these have important places in the myths, while some others are mentioned only once along with their function.
The most perplexing God of Asgard is Loki. He was probably originally a fire God, but he is best known as the troublemaker of Asgard. In various minor scrapes Loki arranges to get the Gods into trouble, usually by giving away their treasures and then arranging to return them. This is very much in the traditional role of a trickster, who keeps things interesting by causing trouble. However, it's sometimes difficult to see Loki merely as a trickster because his actions are sometimes simply too evil to be ignored. Balder was the most beautiful and beloved of the Gods and a pledge was extracted from all the things in the world that they would not harm him. The sole exception to this was the mistletoe which was deemed too tiny to be a threat. Amused by his invulnerability, the Gods took turns throwing objects at Balder, which of course had no effect on him. Loki took the blind God Hod and put a spring of mistletoe in his hands and guided him to throw it. The dart pierced Balder's breast and he died. Later a deal was arranged wherein Balder would be allowed to return to life if all the creatures of the world would weep for him. Only one refused, an ogress who said she cared not a whit for Balder when he was alive and thought him just as well off dead. The ogress is believed to have been Loki in disguise. For these actions Loki was chained beneath the earth and it was arranged that venom would drip upon him in punishment that would last until the end of the world. With the death of Balder, Loki goes beyond the level of trickster and becomes a truly evil figure. It is known that when Ragnarok comes, Loki will lead the legions of chaos against the Aesir and bring about the end of the world.
Indeed Loki's actions certainly do seem harsh, but they are entirely in keeping with the Norse way of looking at things. One of the functions of a trickster God is to keep things from becoming stagnant. The trickster causes trouble so that people may evolve, for nothing brings about ingenuity like need. The Norse did not believe anything was eternal. In the end even the Gods would die in the battle of Ragnarok, which would also destroy the world. Balder's invulnerability was not natural. As the Edda says "Cattle die, and men die, and you too shall die..." It was deemed much more wise and valiant by the Norse to live up to one's fate than to try to avoid it. It would likewise be unnatural to return from the dead. One can see Loki as merely acting as an agent of nature to return things to their normal and correct course. In such a view, it was not an act of evil, but an intervention to stop an evil against the natural order. Likewise Ragnarok must come. It is in the nature of the world to be destroyed and then be reborn.
On the other hand, Loki is a God of darkness. As far as we know Loki was never worshipped, at least not in the same way as the other Gods were. Recognition of his action and his place in the universe is essential, but Gods of this type are seldom welcome. It is "fashionable" today to laugh at trickster Gods and see them as a sort of jester figure, but we must not forget that their nature is much darker than this even when it does serve a purpose. Change is important, but nothing changes the world faster and more thoroughly than war.
While seldom reckoned today among the most popular of the Gods, Tyr is extremely important. He is the God of battle, of justice, and (secondary to Odin) of Kingship. The most important myth concerning Tyr shows both his bravery and honor. He gave his hand as surety to the Fenris Wolf that no trickery was involved in the Gods binding of him. When the fetter in fact did bind the wolf, Tyr lost his hand. The honor and reliance on ones word is often overlooked in this myth in favor of an interpretation of self sacrifice. However, throughout the myths various deals are made and the Aesir easily get out of them. It's likely that Tyr could have escaped his fate as well, but one's word is one's word and thus Tyr lost his hand because it was less valuable to him than his honor and word. Tyr was held to be the God of the Thing or assembly. While the ancient Norse were not truly democratic, and in fact held slaves, within the noble class all were reckoned to be roughly equal. The Thing was a place where the landholders would meet for trade and to iron out disputes among them, in the hope of avoiding feuds. Tyr was originally the chieftain of the Aesir and the God of Kingship, but he has been gradually supplanted by Odin, especially during the Viking Age. It is likely this was because of Tyr's strong sense of honor and justice. For raiding and pillaging, Odin, the God of the berserker rage, was a much better patron than Tyr, the God of honorable battle. This is an important thing to note about Northern religion: it is extremely adaptable. There are not hard and fast rules about who is what and while the nature of the Gods cannot be changed they are more than happy to have the aspects most important to their worshippers emphasized. Just as a person uses different skills and "becomes a different person" when they move or change jobs, so the Gods too have adapted to new climates and needs.
While we only know the myth of Balder's death, it is clear that he was a God of some importance. Unfortunately, modern writers, coming from a Christian background, have tried to turn Balder into a Christ figure. Balder was a God of beauty and goodness, but his name also translates as "warrior." It is a mistake to turn him into a "Norse Jesus." The mere fact that he died and will return after Ragnarok is not enough for this equation. Another interpretation of Balder is that of the dying and resurrected God of the Sun. This also seems a mistake, as Balder does not return from the land of death. It makes a poor symbol to honor Balder on solar holidays, lest the sun not return! The remaining major interpretation of Balder is as a God of mystic initiation. While this fits to some extent, we unfortunately no longer know. The equation with Christ has wiped out a great deal of lore about Balder and we are left to rediscover his place in our modern practice.
Of the other important Gods, Heimdall is the guardian of Asgard. He, as Rig, is also one of the Gods who fathered mankind. Heimdall will sound the horn warning of the final battle of Ragnarok. Njord is the God of sailing and sailors. Unless one travels on the sea, he is probably of little importance to you, but if one does sail, he is your natural patron. If Njord is the God of sailing and of man's use of the sea, then Aegir is the God of the sea itself. He is married to Ran who takes drowned sailors to her home after their death. Aegir is considered to be the greatest of brewers, and our kindred honors him in a special holiday due to the importance of mead in our modern religion. Bragi is a much overlooked God who is the patron of taletellers and bards. Other Gods more or less overlooked in the myths include Forseti, who renders the best judgments, Ull, a God of hunting who is the male counter to Skadi, Vithar, the son of Thor who is as strong as his father, Vali, Odin's son who will avenge his fathers death at Ragnarok, and Hod, the blind God who was led to slay Balder.
While we might say that certain Gods are more important than others, this is in many ways not accurate. We would be better served to say that some are more popular. The Norse concept of the relationship between men and Gods was one of friendship. A man would honor all the Gods as worthy and existent, but would usually find one as his special patron. It is not surprising, considering this, that Thor is the most popular of Gods. If the average person was searching for a God very much like himself, Thor would be the obvious choice. Likewise, a God such as Njord would have been extremely important to sailors and fishermen, but would have been almost completely unimportant as a patron to inlanders. The less well known Gods are just as powerful as their more well known contemporaries, they merely have power over a less well known aspect of life.
There are also many Goddesses other than Frigg and Freya, but we know very little of them. Eir was said to be the greatest of healers, and is for this reason very important. There is no healer God as the ancients held that medicine was a craft for women and not for men, but modern male healers should certainly invoke her. While Skadi has a very small part in the myths, many modern Asafolk find her a compelling figure. She is the snow-shoe Goddess, who travels in the isolated mountains hunting with her bow. She is married to Njord, but they are separated as Njord can't abide the mountains, and Skadi can't sleep in Njord's hall where she is kept awake by the pounding of the sea. She is an excellent role model for women who work alone and who are independently minded. Oaths are sworn to the Goddess Var, but little else is known of her. Lofn might some day be of importance to you, she is known to bring together lovers who are kept apart by circumstance.
I have merely touched upon the Gods here. It is important for everyone who would practice the religion of the North to get to know the myths and the Gods. An appendix is included which outlines various sources for more information.
The Jotnar or giants are the sworn enemies of the Gods. While the Aesir represent order and the Vanir represent the supportive powers of nature, the Jotnar represent chaos and the power of nature to destroy man and act independent of humankind. In the end, it is the Jotnar who will fight the Gods at Ragnarok and bring about the destruction of the world.
In essence despite being called Giants or Ogres, the Jotnar are Gods just as much as the Aesir or Vanir. In many cases they correspond very closely to the Fomoire in Celtic mythology. Most simply put, the Jotnar are the Gods of all those things which man has no control over. The Vanir are the Gods of the growing crops, the Jotnar are the Gods of the river which floods and washes away those crops or the tornado which destroys your entire farm. This is why they are frightening and this is why we hold them to be evil.
The Jotnar are not worshipped in modern Asatru, but there is some evidence that sacrifices were made to them in olden times. In this case, sacrifices may very well have been made "to them" rather than shared "with them" as was the case with the Vanir and Aesir. It would be inappropriate to embrace them as friends and brothers in the way we embrace our Gods. One doesn't embrace the hurricane or the wildfire; it is insanity to do so.
As I've suggested earlier, the Jotnar aren't grouped so much by their commonalities, but by their non-membership in the Aesir. Thus, some of them are benign, while others are apparently evil to the core. Aegir, Skadi, and several of the wives or mates of the Aesir are from Jotnar stock. Others, such as those appearing at Ragnarok, seem to have no redeeming characteristics and are entirely hostile.