The parable prodigal son is from one of the Gospels, which were written by one of the 4 evangelists: Matthew, Mark, Luke, and John, which tell the story of Jesus' life.
The story has a rich man who has 2 sons. The younger son asked for half the money and then wasted it, becoming poor after. He comes back to his dad asking for forgiveness and his dad accepts him and celebrates that he has realized what he did was wrong. The older brother gets mad that their father forgave the younger son as the younger son made many mistakes, but his dad explained that he was willing to forgive him.
The moral of this story (in a sense of Christian faith) is that no matter what you do wrong, even if it is a extremely evil sin, if you are truly sorry and wanting to repent, God will always accept you and forgive you.