Apollo was originally associated with arts, such as music and poetry, but was later transfigured into the god of the Sun, overshadowing Helios. He is the son of Zeus, the king of gods, and Leto, a mortal woman. He is also the twin brother of Artemis. Apollo's skill in music is also known to be unmatched. Before he and Artemis' birth, the jealous Hera had made all land shun her so she was unable to find a place to give birth.
But Poseidon took pity on Leto and showed her an island that was not attached to the sea floor so it technically was not considered land. So Leto traveled there and gave birth. The little floating island is called Delos. Since Apollo was the god of prophecy he decided that he needed a place where mortals could come and ask questions to him and he would use his gift of prophecy to answer them.
He found a perfect place called Pytho. The only bad part was that a terrible, giant snake called Python was living there and was terrorizing all the other living creatures there. So he killed the snake and renamed the place Delphi. He created his temple and the oracles spoke to the mortals prophecies in which Apollo would give to them to give to mortals.