I'm inclined to start here for no other reason that I think these guys influenced a number of other creation stories and many of the religions that began in the fertile crescent - they had the original flood story. Okay here's the skinny on how the world got going. An (Heaven) and Ki (Earth) - the original gods and the parents of the other gods - united to form Anki (the universe). The other gods came along later and began right off intermarrying. The children of these gods thought the necessary task of farming was too difficult so they created humans. This was done by the Nammu (goddess of the water) who put her son to the task of making people. Once the humans started in on farming the gods organized the Tigris and Euphrates so the job could be easier. Strangely, it was the trickster god Enki, a notoriously lazy fellow, who got most of this going. Rumor has it that he used his penis to fill the rivers and streams. He also wanted to use that same penis to impregnate the maiden goddess Uttu but she would not agree until he invented vegetation - fruits and vegetables. He must have wanted her pretty bad because he presented her with three of his inventions: apples, cucumbers, and grapes. She gave in and their offspring invented all the other fruits of the fields.
Let's go to another part of the world to see how they started everything. Whereas Sumerians used sex to begin the world - they revered the sexual act as divine, Scandinavians used a combination of sex and murder (strangely enough the Greeks started creation with a patricide).
Norse - When the void, or at least near-void existed there were three regions: Mudspell in the south - all molten rock and inhabited by a demon named Black Surt who wielded a flaming sword always ready to destroy anything even remotely looking like creation. Niflheim in the north, all ice and frost. And finally between them both Ginungagap, a wet place of rivers but still kind of sterile. In this middle region was born a frost giant named Ymir, who had a propensity for other beings to spring out of his orifices. An man and a woman sprang out of his armpits. A family of frost giants emerged from between his legs. From his middle came the first cow, Audumla.
Audumla licked at the borders of ice around the rivers and Buri, one of the original gods came forth. He married one of the frost giants and they had a son, Bor. Bor married Bestla, another frost giant - I guess the gene pool was kind of restricted. But here's where things get interesting. Bestla had three children Odin, Vili, and Ve. These guys must have been born belligerent because the first thing they did was kill the original Frost Giant Ymir and from his flesh and bones they created the world. His blood made the oceans and lakes. The sky came from his skull. They made the walls of Mitgard (that's the Earth for you people who didn't see the movie Thor) from his eyebrows - imagine that! They then created Embla, the first woman (I know. I thought a woman sprang from Ymir's armpit) and Ask, the first man. I guess it was a big deal to have dwarfs because they were created out of the maggots feasting on Ymir's flesh. Mitgard was given to these two as their home and they went straight about making all the people who came after. Asgard the home of the gods was the last thing to be created. Of course, in the middle of all this creating there were heavenly wars, ...and more wars...and more wars. Vikings loved to fight.
Coming attractions - Native American and Chinese Creation Stories. Stay tuned.