Right now you might be saying, "What free gift??"
It's the gift of "salvation" - but what is salvation? First, let's see what salvation is not. Salvation is not the same thing as "religion."
Did you know that God hates religion?
That's right - when you have a girlfriend or boyfriend (or you get married), do you want a "religious experience" with that person, or do you want a relationship with them? You want a relationship, of course! The same holds true with God - He just wants a one-on-one relationship with you, like you would have with a friend. The difference is, there's no way to "earn" this gift of a relationship with God, because it's free. In fact, the Bible says that it is "by grace you have been saved through faith... it is the gift of God, not of works, so that no one can boast," (Ephesians 2:8, 9). Do you remember when you were younger? At Christmas when your mom or dad gave you Christmas gifts, did you have to pay for them? Of course not. The same holds true with God.
But what if you're already a "good person?"
Maybe you already believe in God, haven't killed anyone, and all that? Why should you care about salvation? First of all, there's no such thing as a "good person." God says in Romans 3:23 that "all have sinned and fall short of the glory of God." We are all separated from God by sin - until we ask Jesus into our hearts. Secondly, it isn't enough to just believe there is a God. Jesus said that unless you are "born again," you cannot see the kingdom of God (John 3:3). Being "born again" means more than just believing that Jesus Christ/God exists - it means asking Jesus into your heart by faith, totally relying on what He did on the cross for you. He has forgiven all of your sins.
So you think that you've done some "horrible" things?
You're a "bad person"? You might be thinking that there's no way God could forgive you. The truth is, God says in John 6:37 that anyone who comes to Him will not be cast out! Remember that if you could save yourself (by being "good," or becoming a church member, or even by being water-baptized), there would have been no point in Jesus dying on the cross. He died because there is no way you can save yourself.
"So what now?"
To receive God's free gift of salvation, you just need to ask Him for it. Pray this prayer - based on Romans 10:9, 10 in the Bible:
"Jesus, I confess that I need You. My own works are not good enough. I have sinned, and I need to receive this free gift. I confess you as Lord, and believe in my heart that God raised you from the dead. Lord Jesus, fill me with your Holy Spirit; guide me to a Bible-believing church; and help me to read your Word. Thank you for dying for me."
You are now a born again Christian.
Remember, you're not "religious." Instead, you have a personal, one-on-one relationship with God. You can think of God the Father as your "spiritual dad" (remember He is a good Father). Think of God the Son (Jesus) as your Lord and Savior - as your "best friend." Think of God the Spirit (the Holy Spirit) as the Spirit of God that lives in you. Think about it - God actually wants to live "in you"!
If anyone ever comes to you and asks if you're sure that you're going to Heaven, you can say "yes," because of what Jesus did on the cross! Think about this verse from the Bible, found in 2 Corinthians 5:17. "Therefore if anyone is in Christ, He is a new creation; old things have passed away; behold, all things have become new." Now you can live not by how you "feel," but by who God says you are. God says you are now His son or daughter (Galatians 3:26, 27)!