A witch owns a garden, which Rapunzel's parents steal from. As punishment for this, the witch takes their first-born and names her Rapunzel, after one of the flowers they stole.
At the age of 12, the witch locks Rapunzel up in a tall door-less tower and refuses to let her see anyone else. As years go by, Rapunzel develops an amazing singing voice (learning from birds), and an incredibly long head of blonde hair that the witch forced her to grow as a means of accessing the tower.
One day, a Prince happens upon the tower and sees how the witch can climb her hair. The Prince calls down to her, and she lets down her hair, thinking it's the witch. He learns that Rapunzel has been imprisoned in the tower by the witch. The Prince decides to altruistically rescue her.