[BridgesAndBalloons]

To the best of my knowledge you basically say a prayer. I was raised an Evangelical Christian and people said the Sinner's Prayer in a Church. I'm not sure how other branches of Christianity do it, I think it's something you can do at home just between you and God. Just by talking to him asking him to forgive your sins etc.

Then the next step is living the rest of your life being devoted to God and loving him more so than anyone/anything else on earth.

I found an example of a Sinner's Prayer;

"Heavenly Father, have mercy on me, a sinner. I believe in you and that your word is true. I believe that Jesus Christ is the Son of the living God and that he died on the cross so that I may now have forgiveness for my sins and eternal life. I know that without you in my heart my life is meaningless.
I believe in my heart that you, Lord God, raised Him from the dead. Please Jesus forgive me, for every sin I have ever committed or done in my heart, please Lord Jesus forgive me and come into my heart as my personal Lord and Savior today. I need you to be my Father and my friend.

I give you my life and ask you to take full control from this moment on; I pray this in the name of Jesus Christ."