There are multiple stories. I learned both of these. It's been written down a thousand times, leaving thousands of different stories.Listen up you freaking failures of Greek mythology. It all started when there was a time that the Titans (Titanes) became rulers of the earth. There was a leader among these Titans, and his name was Cronus. When his wife (Rhea) bared all of his children, he was visited by a Faith, (a fortune teller by our standards, who's visions always became mostly true.), and she told Cronus that one day he would be killed by one of his children. Enraged Cronus ate "all" of his children. He ate one by one throughout days and his wife became fed up with him eating all of their children, so she replaced Zeus with a rock and Cronus ate it thinking that all of his children were right inside his belly. Later Zeus grew up on the island of Crete. After he became an adolescent, he obtained a potion that induced vomiting from a female Titan named Metis. Zeus had his mother Rhea arranged for him to become his father’s cupbearer. He slipped the potion into a drink causing Cronos to spit up his brothers and sisters. The five siblings were so grateful for the rescue that they wanted Zeus to become the leader of the Olympians. Cronos feared the rising power of Zeus. He tried to rally the Titans to join him to defeat Zeus and his siblings. He was not able to get the Titan women to join him. Two of the men, Prometheus and Epimetheus actually joined the Olympians against their fellow Titans. The rest of the Titan men chose Atlas to lead the battle against the Olympians. For ten years, the Titans and the Olympians fought with neither side able to gain a lasting advantage. Gaia advised Zeus to free the Cyclopes and the hundred headed Giants from Tartarus (a place in the underworld) and persuade them to join his side. Zeus went down to Tartarus, killed the monster which guarded the prisoners, and released them. In return for their freedom, the Cyclopes and the Giants became allies with Zeus tipping the scale of power to the Olympians. The Cyclopes gave Zeus the power over thunder and lightning. Then gave the helm of darkness to Hades and to Poseidon they gave a trident (three-pronged spear). Hades used the helm of darkness to steal away Cronus’ weapons and Poseidon came at him with the trident. The distraction allowed Zeus to strike with lightning, and he downed Cronus. With the defeat of Cronus and the added power of the Cyclopes and Giants, the Olympians were able to defeat the Titans. The Titans who participated in the war, were imprisoned in Tartarus. Atlas was given a special punishment for his role in the war. He was required to hold up the sky.
There you go. NOW YOU KNOW HOW THE TITANS LOST.