The verb repent means "to feel sorry for something you've done." When you repent, you acknowledge what you did and vow to change your ways.
The word repent comes from the Old French word repentir, which means, "to feel regret for sins or crimes." If you cheat on an exam in school, and feel guilty afterwards, you might repent for your bad behavior by confessing to your teacher. The verb repent is often used in a religious context: when you repent, you try to make up for what you've done, promise to avoid sin in the future and devote yourself to God.