It is said that Poseidon was swallowed whole by his own father, Cronus. But Zeus, his hidden brother, got the help from the Goddess Metis who gave Cronus a potion to drink that will make him throw up all of his children, and he did. Zeus overthrew him.
Zeus, Poseidon, and Hades did a draw to figure out who would be the God of something. Poseidon ended up being God of the Sea, earthquakes, floods, droughts, and anything involving water, Zeus the God of the Sky and all Gods, and Hades the God of the Underworld. Poseidon was worshiped by seamen.
Poseidon then married Amphirite, one of the granddaughters of Oceanus, the Titan. But, Poseidon started to desire Demeter, so to deter him, Demeter told Poseidon to make the prettiest animal the world has ever seen, so he made the first horse ever. But, it took him a while, so by the time he made a horse his desire for Demeter was gone.
A Life Lesson
Poseidon was also the God of Earthquakes. His weapon was a Trident that could make the Earth shake, which causes Earthquakes. His Trident was made for him during the Titanes War from the Cyclopses. With his Trident Zeus, Hades, and himself defeated the elder Gods. His Trident is so strong, it can shatter any object. But, he wasn't as powerful as Zeus. Poseidon was second in power to Zeus amongst the other Gods.
After that, Poseidon entered a contest to have control over Athens. Poseidon entered the contest with Athena, a goddess. Poseidon produced the very first horse as a gift, but the King refused Poseidon the land of Athens, so Poseidon created a drought in Athens.
Poseidon entered a contest to have control over Athens, and he lost. Out of anger, Poseidon caused a drought in Athens. Because of his actions, we can learn from him not to get mad or sad (even though he got mad),whenever we lose because it doesn't show a good personality/ behavior.