Well Harry Potter dies because Voldemort uses the Avada kadava curse on Harry.He comes back because Harry was a horcrux Voldemort never meant to create, so when harry died a bit of voldemort died...
Tom Marvolo Riddle - alias Lord Voldemort - wants to kill Harry in the end of The Deathly Hallows, but the curse falls back to himself. Voldemort tried to kill Harry Potter with the Avada Kedavra...