In the beginning, Chaos was surrounded by an unending stream of water that was ruled by the God Oceanus. The Goddess Eurynome desired to make order out of Chaos. By mating with Ophion (Sometimes North Wind, depending on the version you're reading), she gave birth to Eros, who was also known as Protagonus.
Eurynome separated the sky from the sea by dancing on the waves of Oceanus. By doing so, she created great lands to wander. It was then populated by creatures such as Nympths, Furies and Charites, among other beasts and monsters.
By separating Chaos she created Gaea, Uranus and Tartarus. Gaea and Uranus married, followed by giving birth to the Titans. They warned Cronus of a prophecy that his own children would rise up against the Titans. He responded by swallowing his children before they could grow.
Cronus' wife, Rhea, was giving birth to a sixth child when Gaea had an idea to save her grandchild. She took a stone, wrapped it in swaddling clothes, and offered it to Cronus. Thinking the stone was the child, Cronus swallowed it.
Gaea was able to hide the baby, named Zues, in what is now called Crete. With time, Zues grew up, and searched for his parents. He immediately fought with Cronus, who had no idea Zues was his own offspring.
Metis, Zues' first wife, found a way to administer an emetic to Cronus. Zues' older siblings, Hestia, Demeter, Hera, Hades and Poseidon joined Zeus agasinst ther father. They defeated the Titans after a long war, followed by dividing up the universe to bring further order out of Chaos.
Zeus made himself Supreme God over all the other Gods and Goddesses, as well as the mortal beings that wandered over the Earth. He also created a palace for his favored Gods on Mount Olympus in Thessaly. The rest were left to fend for themselves in lands below Mount Olympus.
Zues decided he should be God of the Sky and all associated phenomena. Hestia became the Goddess of the Hearth. Poseidon was given rule over the Sea. Demeter became a Fertility Goddess, and many things associated with fertility. Hera was Goddess of Marriage and Childbirth. And finally Hades was made God of the Underworld.
Zeus, however, did not like the humans. He did not find them beautiful, and being mortal was another strike against them. They also complained about the lack of good food and the cold nights, which annoyed Zeus. He chose to ignore them, while he and the other Gods feasted and enjoyed hearths in every room of their palaces.
Prometheus, who was one of the Titans that did not fight against Zeus, took pity on the humans. He stole some of the sparks from a fire on Olympus and gave it to the humans.
Zeus was furious at the insult to his power, and had Hephaestus fashion a creature to torment Prometheus. It was a woman they named Pandora. She was given a precious and beautiful box, which she was told not to open. But her curiosity won, and she opened the box. All the evils of the world were released, but she managed to close the box before Hope could also escape.