Okay kiddo, the story of the liberation of Peter is from the Bible, and it goes like this - Peter was a follower of Jesus and he was put in prison by a mean king. The king didn't like people who followed Jesus and he wanted to punish Peter, so he put him in a big room with guards at the door so he couldn't escape.
But, one night, while Peter was sleeping, an angel came to help him! The angel made the guards fall asleep and helped Peter sneak out of the prison. Peter followed the angel's instructions and escaped safely.
When Peter got out, he went to his friends who were also followers of Jesus and told them what had happened. They were amazed and knew that it was a miracle from God.
So, the liberation of Peter means that he was set free from prison by an angel sent from God. It shows us that God is always watching over his followers and will help them in times of trouble.