The Theogony is a large synthesis of the wider local Greek traditions concerning the gods' origins, organised as a narrative.
Note:This is just a brief summary.
The poem starts with a blessing from the Muses and thanks them for inspiration.
Cosmogony and Castration of Ouranus
Chaos was the first to come to be, followed by Gaia, Tartarus and Eros. From Chaos came forth Erebus and Nyx, and from Nyx and Erebus came Aether and Hemera. From Gaia came Ouranus, the Ourea and Pontus.
Gaia then lay with Ouranos and bore Oceanus, Coeus, Crius, Hyperion, Iapetus, Theia, Rhea, Themis, Mnemosyne, Phoebe and Tethys. After them Cronos was born. After that she mated with Ouranos once again, and bore the Cyclopes; Brontes, Steropes and Arges, who made thunder for Zeus. She also had the Hecatonchires; Kottos, Briareos, and Gyges. Ouranus was disgusted with them and hide them away in Earth. She asked the Titans to punish their father. Cronos volunteered and castrated him with the sickle his mother had given him.