Odin and his brothers, Vili and Vé, create Middle-Earth (the world of humans) from the body of a giant.
The three brothers kill a giant named Ymir. (No wonder the Aesir gods and giants don't get along.)
They create the world from his body, using the different body parts to make different things:
From his flesh and some of his bones, they make the land and rocky mountains.
They use his blood to make the sea and other bodies of water.
Ymir's teeth and some of his bones become gravel and boulders.
The three brothers place Ymir's skullcap above the earth and place a dwarf at each of the earth's four corners. These dwarves are named North, South, East, and West.
They use Ymir's eyebrows to create a protective fortress around the earth, in order to prevent the giants from ever entering it. They call this place Midgard, or Middle-Earth.
From Ymir's brain, they make the clouds.
They make a place for the sparks that are shooting out of Muspelheim, the primordial fire-world that they have now separated from the earth. These sparks become the stars, sun, and moon.
The dark and beautiful daughter of a giant, Night, has a son with one of the Aesir gods, a bright and radiant boy named Day.
The gods give Night and Day chariots and horses and place them in the sky, ordering them to ride around it.
The sweat dripping off the mane of Night's horse causes the dew each morning.
Day is so bright and hot that the gods must attach bellows (blowers) to his horse's legs to keep them from burning up.
A witch that lives to the East of Middle-Earth gives birth to two giant sons in the shape of wolves. The wolf-giant Skoll chases the sun as his brother Hati chases the moon. These brothers keep the sun and moon racing around the sky, creating the cycle of day and night.
From the maggots growing in the dead body of Ymir, Odin and his brothers create the race of the dwarves. (Gross, we know. We're not sure Gimli would appreciate this.) Dwarves live in caves beneath the earth and supply the gods with iron, silver, and gold.
Odin and his brothers create other races: the light-elves, who live far above the earth in Alfheim; sprites and spirits, who populate the forest groves and streams; and animals and fish.