What is Baptism? Baptism is the sacrament that gives our souls the new life of sanctifying grace by which we become children of God and heirs of heaven.
Amen, amen, I say to thee, unless a man be born again of water and the Spirit, he cannot enter into the kingdom of God. (John 3:5)
What sins does Baptism take away? Baptism takes away original sin; and also actual sin and all the punishment due to them, if the person baptized be guilty of any actual sins and truly sorry for them.
Get up and be baptized and wash away thy sins, calling on his name. (Acts 22:16)
Further reading: CCC 1213-1222