In the beginning, there was Chaos. Then, out of Chaos came Erebus, Nyx, and Eros bringing the start of order. From Eros came Aether, and Hemera. Once there was Aether and Hemera, Gaea appeared. Gaea alone gave birth to Uranus, who became Gaea's husband. Together they produced the three Cyclopes, the three Hecatoncheires, and twelve Titans.
Uranus was not a good father nor husband. He hated the Hecatoncheires so he imprisoned them in Gaea's womb. This made Gaea angry so she plotted against Uranus by getting the youngest Titan, Cronus, to overthrow him.
Cronus became the next ruler, but became paranoid that one of his children would overthrow him, like his father before him, so he ate them. His wife, Rhea, concealed a baby (Zeus) by switching him with a stone in a swaddling cloth. She was able to pass off the rock as the baby. Cronus was fooled and swallowed it.
Zeus overthrew Cronus with the help of all his brothers and sisters that were in jail. After overthrowing Cronus and his siblings, they became rulers of the gods.
Zeus killed the Titans who fought against him, except for Atlas, who was forced to hold the world on his shoulders forever.