Ooh, story time is my favorite time. Sitting around the camfire, sharing tales. This will be condensed, so some details are left out.
Ahem. A long, long time ago in a galaxy far away..
There was nothing. No Earth, no Heaven, no sky, no land, no water. There was nothing, just a void which we call Ginnungagap. North of this there lay Niflheim, the world of ice, and from this cold and dark place flowed the river Elivagar. As the water of the river came south it cooled, hardening into a thick ice. Further south was Muspellheim, the world of fire. Over time, the northern part of Ginnungagap became filled with a thick, cold ice. The southern part, however, was kept warm by the flames and sparks flying off of Muspellheim. The heat and coolness met in the center of this void, and there began to thaw the heavy icy. And as it thawed, a figure appeared. The first being to come from this land, called Ymir.
As the ice continued its thaw, another figure appeared: a giant cow, named Audhumbla. Her teats were the source of rivers of milks, and from here Ymir fed. He slept, unaware and unconscious. But as he slept, two giants grew from his armpits and one six-headed giant sprung from his legs. Meanwhile, Audhumbla licked the ice and melted it down until eventually a mans head appeared. Over time, the man was freed from the ice. He was known as Buri, the first of the Aesir. He soon married Bestla, a descendant from one of the giants birthed by Ymir. Through time, he had three sons: Odin, Villi and Ve.
Eventually there came great conflict between the giants birthed from Ymir and the children birthed from Buri. Odin then led his two brothers against Ymir. This was the original act that sparked hatred between the giants and the Gods. They killed him then tore apart his body. His flesh became Earth, his blood became sea, his hair became trees, his bones formed mountains and his teeth were made to stone. Maggots crawled in Ymirs flesh, and these later became the alfar and dwarves who reside deep in the Earth.
As the blood of Ymir flowed across the land it killed all of the giants except for one family, whom escaped in a boat. This family is the original source for all of the following etinfolk that exist today. They escaped to a world named Jotunheim, where the giants dwell now.
Odin and his brothers continued fashioning the heavens from Ymirs corpse. They fashioned Midgard, where humans exist, from his eyebrows. His brains were thrown into the air and become clouds. They built themselves a stronghold, called Asgard, and a bridge, called bifrost, connecting it to Midgard. They created the sun, moon, and stars in the sky.
One day, it is said that Odin and his brothers walked along the sea shore when they discovered two tree trunks. Odin gave them soul, Ve gave them being and Villi gave them motion/sense. And so, the trunks formed the first two humans: Ask and Embla.
And there is a short summary of the creation story.