If you believe that Jesus saves you from sin, confess your sins to Him, and acknowledge that is Lord of all, then you are a new person inside. Sin will no longer control you, and you are guaranteed eternal life in heaven. Jesus is your Saviour and Lord. How do you know? Because God promised, and God always keeps his promises. Although your relationship with Jesus as the Saviour and of you life begins at a moment in time, you should have an active, daily trust in Jesus Christ that continues throughout your life.
Romans 10:9-10:
Verse 9: That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
Verse 10: For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.