Gaia and Uranus had three sets of children: the giants, the Cyclopes, and the Titans. The titans were the more humanoid of the three, and among their number was the Titan of Time, Cronus (also known as Kronos, or Saturn, sort of also Chronos/Khronos, but that gets complicated).
Uranus was a terrible father. He tried to take the children from Gaia and imprison them. So she plotted with the Titans against Uranus. Gaia gave Cronus, the youngest of the Titans, a flint and a sickle to use against his father. Cronus fought Uranus and castrated him. His nether bits fell into the ocean and from their blood sprang the furies, from the foam came Aphrodite.
This act might have been where the name Titan came from. Kind of like how Trump brands everyone he doesn’t like with a pejorative, Titans may have come from a source word that meant strained ones, but Hesiod is alone in that interpretation.
In some versions of the myth, it’s not Uranus that Cronus overthrew at all, but a serpent who was trying to devour the world called Ophion.
Whatever Cronus hit with that sickle, the imagery stuck. That sickle became Cronus’s calling card and made it into almost every image of Cronus ever produced. Because of that, he was frequently associated with the harvest and had an entire day dedicated to him around harvest time.
all the myths agree that the period of time when he ruled was called the Golden Age, because for a short time, there were no rules. Everyone just did the right thing because it was the right thing to do. Who “everyone” was is kind of unclear. Man shouldn’t have been around at this time, except in some versions of the myth they were. There were a lot of Titans, but a lot in the sense that it would be a crowded classroom, not a crowded school. It would have been a fairly manageable crowd given that he’d sent anyone who might even consider disagreeing with him, like the Giants and the Cyclopes, into Tartarus and ate any children who may decide to shake things up in the future.
Rhea and Cronus had five children before Rhea got tired of her babies getting devoured. When child number six was born, Rhea tricked Cronus and gave him a stone instead.
That child was Zeus.
Because Cronus ruled the earth and the sky, Zeus had to be suspended from the ground by a rope so he was never fully in either realm. He grew up this way and when the time was right, went against his father to avenge his siblings.
He managed to trick Cronus into drinking a potion that made him vomit up Zeus’s siblings. These children were Hera, Poseidon, Hades, Hestia, and Demeter. Zeus also freed the giants and the Cyclopes. Together, they fought Cronus and most of the remaining Titans and won and Zeus became god of Olympus.
Cronus and the Titans were cast into Tartarus, or possible a cave of Nyx, as punishment for their treatment of the Olympians.
Lifetimes later, Zeus released the Titans and made Cronus the king of Elysium. That’s still in the Underworld, so it’s not like he truly released them. Just relocated their prison to a nicer one. Or if you’re Roman, he became a kind of supreme court judge, settling disputes amongst the gods.