and correcting me
Cronus was told by his father Uranus and Mother Earth that one of his own sons would someday over throw him. Cronus then swallowed the first five children that his wife, Rhea, bore him: Hestia, Demeter, Hera, Hades, and Poseidon to stop this from happening. He meant to swallow the next child, Zeus, but Rhea tricked him and saved the baby. She substituted a stone wrapped in cloth for the baby and gave in to Cronus. Zeus was raised by nymphs and grew to manhood in secrecy of his father. Eventually, he returned home and became cup-bearer for Cronus. After drinking poison mixed into his drink by Zeus, Cronus vomited up his five children and the stone. This is how Poseidon came to the world.
After releasing his brothers, Zeus led a war against Cronus and the other Titans. The war went on for ten years when Zeus, Poseidon & Hades released the Cyclopes from captivity. In gratitude, the Cyclopes gave each of the brothers a weapon. Poseidon received a trident, Zeus a thunderbolt, and Hades a helmet of darkness. They used these gifts to finally defeat Cronus and the rest of the titans. Now that the three brothers were the rulers of all existence they decided to draw lots to determine their domains. Poseidon drew water, Zeus drew the sky, and Hades drew the underworld.
And that is how "The Big Three" got their powers.