There were two ordinances given to the New Testament church, baptism and the Lord's Supper.

Baptism was practiced even before Jesus Christ rose again when John the Baptist would baptize people who got saved.

(Talking about John the Baptist) John 3:6 - And were baptized of him in Jordan, confessing their sins.

The purpose of baptism is to represent what Jesus Christ did when He died and rose again. Baptism comes from a word that means "to cover" or "to immerse." That means that baptism is not done through sprinkling. So, when we are buried underwater, it represents Jesus dying, and then we come out, representing Jesus coming back to life.

Baptism was only done to those in the Bible by those who converted to Christianity, which was always done by people old enough to willingly consent to it. For this reason, there is no mention of infant baptism in the Bible, which was added later as the church believed baptism was necessary to go to heaven.

Baptism is not necessary to go to heaven. In the Bible, the thief on the cross was never baptized, and no one in the Old Testament was baptized. The Bible says that works are not what makes us saved, merely proves it. Therefore, a person can be saved and not baptized.

Titus 3:5 - Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost;

John the Baptist also parallels it when he says that though he baptized by water, Jesus Christ would baptize by fire (the Holy Spirit), showing that what happens inside is what matters in salvation, not what we do on the outside.

Matthew 3:11 - I indeed baptize you with water unto repentance: but he that cometh after me is mightier than I, whose shoes I am not worthy to bear: he shall baptize you with the Holy Ghost, and [with] fire: