Sometimes, the easiest way to get to know things, is from the top down. Things are built from the bottom up, but when dealing with places that have rulers, you learn the name of the King or Queen first, because that will save your life.
In Norse/Germanic religion, there are five such beings that you should know as Rulers of Realms: Odin, Lord of Asgard. Hel, Lady of Helheim, Freyr, Lord of Alfheim, Surt of Muspelheim. And Hreidmarr/Hreithmarr, Lord of Nidavellir (The Dwarf World).
Odin, the Allfather, is probably the one you’ve heard of the most. He is king of Asgard, father to Thor, Baldr, Hodr, and other sons. He is husband to Frigga, Queen of Asgard. The One-Eyed God of magic, poetry, frenzy and fury, battle and death. He is lord of Valhalla, the hall of the slain, where mighty warriors go after death to train and feast till the final battle. Often he is seen as a wanderer, in all circles of society. Gandalf, from Lord of the Rings, was based in both image and temperament upon Odin Allfather. Odin is the God, who along with his brothers Vili and Ve, created mortals and Midgard. He is chief of the Asgardians, the Gods closest to us mortals.
Next up, and just as important as Odin, though less known, is Hel. She is the Queen of Helheim, and some say also rules Niflheim. Odin is the keeper of half the dead the dead that fall in glory to battle, Freya gets the other half, but everyone else goes to Hel. Those that die of old age, sickness, car accidents, meteorites falling from the sky, murder, natural causes, what have you, they go to Hel. The Christian Hell took its name from Hel, but her realm is nothing like the place of burning and torture. It is a calm land, beautiful, just like our world of Midgard. She keeps our ancestors there, safe from all the threats of all the worlds out there, protecting our souls in death from those that would use them for ill or destroy them. Most of us today will not see death in battle, or so it seems at this time, so we are likely to journey to the realm of Helheim when we pass. It would be a good idea to cultivate at least a passing goodwill with its Queen, for she also punishes those who break oaths, who turn against their kin, and who in a religion without any real definition of good or evil…go so far as to be deemed beyond evil.
Then we have Freyr. He is the Vanic God of nature and fertility. He lives with the Aesir, but he is ruler of the world of Alfheim, home to the elves. He, like the world he rules over, is both wild and tame, fertile and dangerous, and the Alfs/Elves he rules over do his bidding as loyal and powerful subjects, seeking to the balance of nature both on their world, and often on our world of Midgard.
Next is Surt, the lord of Muspelheim. Muspelheim is a land of fire, and Surt is a Jotun of Flame. Marvel comics doesn’t get much right about Norse Mythology, but when it comes to Surt they are pretty much right on the mark. If given the choice, do not ever deal with Surt. He is trapped in Muspelheim, and fated to burn the universe should he ever get free.
Last is Hreidmarr, king of the dwarfs. The dwarfs are industrious workers and skilled beyond measure in the making of things. If you are an artisan, you would do well to take counsel from dwarfs and learn from them and make friends. But be warned, Hreidmarr is a greedy king, so in dealing with him rather than his subjects, be prepared to pay a heavy price.
These are the Rulers of the Nine Worlds