Original: Harry learns that his parents were betrayed to Voldemort by their friend Peter Pettigrew, who framed Harry's godfather Sirius Black for the crimes, condemning him to Azkaban, the wizard prison.
Simplified: Harry learns that his parents were sold out to Lord Voldemort by their friend Peter Pettigrew, also accused of framing Harry's godfather Sirius Black for crimes he did n't make, locking him up in the wizarding prison, Azkaban.