Luke spent his childhood years on his uncle's farm on Tatooine.
Luke was never told much about his father, Anakin Skywalker, only that he was a farmer like his uncle.
His life completely changed when he and his uncle bought two droids, R2-D2 and C-3PO. R2-D2 tricked Luke into following him to see a hermit named Ben Kenobi.
When Luke met Ben, he found out the old man's name was really Obi-Wan and that he had an important mission.
Through Ben, Luke learned his father had actually been a Jedi knight and had been killed by an evil Sith Lord named Darth Vader. Luke's uncle and aunt were killed while he was away and when he returned he vowed to help Obi-Wan.