Hopefully making theology simpler to understand! (2 Corinthians 1:12)

And Peter said to them, “Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit.

Acts 2:38, ESV

We let God change our thinking about sin so that we do not want to sin, we believe in the saving work of Jesus, and we get baptized. This is how we become a Christian. It is the work of God by the Holy Spirit.