 You have to ask Him to forgive you for your life of disobedience and rebellion toward Him. You accept the Lord Jesus Christ as your personal Savior, a one-time event in your life whereby you ask Him to save you from your sins and that you're receiving Him as your personal Savior. In that moment, you are forgiven. And the Spirit of God seals you as one of His children. And forever you're one of His children. Will you sin again? Yes.