Okay kiddo, so the sacrament of reconciliation is something that people do in the Catholic Church when they want to say sorry to God for something they did that they shouldn't have done.
When someone goes to confession (which is another name for the sacrament of reconciliation), they talk to a priest and tell him what they did wrong. The priest listens and then tells them what they can do to make things better.
After that, the person says a prayer that says they're sorry for what they did and they promise to try not to do it again. The priest then gives them a special blessing to show that they're forgiven by God.
This is something that Catholics do to help them feel better about themselves and to show that they want to be good people who follow God's rules. Does that make sense, kiddo?