The Norse creation story has heaps of mythic elements, from the primeval giant Ymir to the cow Audhumla the reader is beseiged with mythic archetypes. This is a problem for the researcher trying to sort out true heathen tradition from the trappings of Christianity.
What the Eddas Say
In the beginning there was the void. And the void was called Ginnungagap. What does Ginnungagap mean? Yawning gap, beginning gap, gap with magical potential, mighty gap; these are a few of the educated guesses. Along with the void existed Niflheim the land of fog and ice in the north and Muspelheim the land of fire in the south. There seems to be a bit of confusion as to whether or not these existed after Ginnungagap or along side of it from the beginning.
In Niflheim was a spring called Hvergelmir from which the Elivagar (eleven rivers - Svol, Gunnthra, Fiorm, Fimbulthul, Slidr, Hrid, Sylg, Ylg, Vid, Leiptr, and Gioll) flowed. The Elivargar froze layer upon layer until it filled in the northerly portion of the gap. Concurrently the southern portion was being filled by sparks and molten material from Muspelheim.
The mix of fire and ice caused part of the Elivagar to melt forming the figures Ymir the primeval giant and the cow Audhumla. The cow's milk was Ymir's food. While Ymir slept his under arm sweat begat two frost giants, one male one female, while his two legs begat another male.
While Ymir was busy procreating Audhumla was busy eating. Her nourishment came from licking the salty ice. Her incessant licking formed the god Buri. He had a son named Bor who was the father of Odin, Vili, and Ve.
For some reason the sons of Bor decided to kill poor Ymir. His blood caused a flood which killed all of the frost giants except for two, Bergelmir and his wife, who escaped the deluge in their boat.
Odin, Vili, and Ve put Ymir's corpse into the middle of ginnungagap and created the earth and sky from it. They also created the stars, sun, and moon from sparks coming out of Muspelheim.
Finally, the brothers happened upon two logs lying on the beach and created the first two humans Ask [Ash] and Embla [vine?] from them.