After repentance and faith in Hebrews 6:1 Hebrews 6:1Therefore leaving the principles of the doctrine of Christ, let us go on to perfection; not laying again the foundation of repentance from dead works, and of faith toward God,
American King James Version×, verse 2 lists "the doctrine of baptisms" and "laying on of hands" as two of the elementary principles of Christ.

John the Baptist introduced a baptism of repentance, tied to the concept of forgiveness of sins (Matthew 3:1-6 Matthew 3:1-6 [1] In those days came John the Baptist, preaching in the wilderness of Judaea, [2] And saying, Repent you: for the kingdom of heaven is at hand. [3] For this is he that was spoken of by the prophet Esaias, saying, The voice of one crying in the wilderness, Prepare you the way of the Lord, make his paths straight. [4] And the same John had his raiment of camel's hair, and a leather girdle about his loins; and his meat was locusts and wild honey. [5] Then went out to him Jerusalem, and all Judaea, and all the region round about Jordan, [6] And were baptized of him in Jordan, confessing their sins.
American King James Version×; Mark 1:4-5 Mark 1:4-5 [4] John did baptize in the wilderness, and preach the baptism of repentance for the remission of sins. [5] And there went out to him all the land of Judaea, and they of Jerusalem, and were all baptized of him in the river of Jordan, confessing their sins.
American King James Version×). Jesus Himself was baptized by John (Matthew 3:13-17 Matthew 3:13-17 [13] Then comes Jesus from Galilee to Jordan to John, to be baptized of him. [14] But John forbade him, saying, I have need to be baptized of you, and come you to me? [15] And Jesus answering said to him, Suffer it to be so now: for thus it becomes us to fulfill all righteousness. Then he suffered him. [16] And Jesus, when he was baptized, went up straightway out of the water: and, see, the heavens were opened to him, and he saw the Spirit of God descending like a dove, and lighting on him: [17] And see a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.
American King James Version×), not because He needed to repent of sin or be forgiven, but as an example for His disciples throughout all ages.

The English word baptize is derived from the Greek word baptizo, which means "to immerse." By definition, then, the only biblical form of baptism is a complete immersion in water. John the Baptist chose a particular location in the Jordan River for baptizing because sufficient water was available there to completely submerge individuals (John 3:23 John 3:23And John also was baptizing in Aenon near to Salim, because there was much water there: and they came, and were baptized.
American King James Version×).

For the Christian, the ordinance of baptism is profoundly important. In one action, Christ's death, burial and resurrection are called to mind for the believer and linked to his or her own symbolic "death" and "resurrection" from the "watery grave" to walk in newness of life (Romans 6:3-6 Romans 6:3-6 [3] Know you not, that so many of us as were baptized into Jesus Christ were baptized into his death? [4] Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. [5] For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection: [6] Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that from now on we should not serve sin.
American King James Version×; Colossians 2:12-13 Colossians 2:12-13 [12] Buried with him in baptism, wherein also you are risen with him through the faith of the operation of God, who has raised him from the dead. [13] And you, being dead in your sins and the uncircumcision of your flesh, has he quickened together with him, having forgiven you all trespasses;
American King James Version×).

Also inherent in the symbolism is the promise of the believer's future resurrection into the Kingdom of God. The forgiven sinner emerges from the waters of baptism to live a new life in Christ, free from the death penalty incurred by sin. The waters of baptism have symbolically washed away all sins. In this regard, baptism is an outward acknowledgment of the believer's inward intent to yield and submit his or her life to God and His way (Ephesians 4:20-24 Ephesians 4:20-24 [20] But you have not so learned Christ; [21] If so be that you have heard him, and have been taught by him, as the truth is in Jesus: [22] That you put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts; [23] And be renewed in the spirit of your mind; [24] And that you put on the new man, which after God is created in righteousness and true holiness.
American King James Version×).

Baptism, which is commanded in Scripture, must be preceded by faith and repentance (Acts 2:37-38 Acts 2:37-38 [37] Now when they heard this, they were pricked in their heart, and said to Peter and to the rest of the apostles, Men and brothers, what shall we do? [38] Then Peter said to them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and you shall receive the gift of the Holy Ghost.
American King James Version×; Mark 16:16 Mark 16:16He that believes and is baptized shall be saved; but he that believes not shall be damned.
American King James Version×). The very symbolism of baptism itself shows a willingness to "bury" the old sinful life (Romans 6:11 Romans 6:11Likewise reckon you also yourselves to be dead indeed to sin, but alive to God through Jesus Christ our Lord.
American King James Version×). Our acknowledgment of guilt and the need for Jesus Christ to save us from the consequences of sin is of paramount importance. This repentance is characterized by a change of heart and action and is based on personal faith in, and a total commitment to, Jesus Christ and God the Father (Luke 14:25-33 Luke 14:25-33 [25] And there went great multitudes with him: and he turned, and said to them, [26] If any man come to me, and hate not his father, and mother, and wife, and children, and brothers, and sisters, yes, and his own life also, he cannot be my disciple. [27] And whoever does not bear his cross, and come after me, cannot be my disciple. [28] For which of you, intending to build a tower, sits not down first, and counts the cost, whether he have sufficient to finish it? [29] Lest haply, after he has laid the foundation, and is not able to finish it, all that behold it begin to mock him, [30] Saying, This man began to build, and was not able to finish. [31] Or what king, going to make war against another king, sits not down first, and consults whether he be able with ten thousand to meet him that comes against him with twenty thousand? [32] Or else, while the other is yet a great way off, he sends an ambassador, and desires conditions of peace. [33] So likewise, whoever he be of you that forsakes not all that he has, he cannot be my disciple.
American King James Version×; Colossians 2:12 Colossians 2:12 Buried with him in baptism, wherein also you are risen with him through the faith of the operation of God, who has raised him from the dead.
American King James Version×). 

Baptism should be entered into only by someone who is mature enough to fully grasp and appreciate the lifelong commitment required. The Bible gives no indication that baptism is appropriate for children.

The commission Jesus gave His disciples includes the authority to baptize believers (Matthew 28:18-20 Matthew 28:18-20 [18] And Jesus came and spoke to them, saying, All power is given to me in heaven and in earth. [19] Go you therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: [20] Teaching them to observe all things whatever I have commanded you: and, see, I am with you always, even to the end of the world. Amen.
American King James Version×). Baptism is followed by prayer and the laying on of hands by one or more of God's duly ordained servants. This demonstrates that God acts through human servants and that we are to cooperate with the faithful ministry He has established in His Church.

This is all part of the process by which we receive the gift of God's Spirit (Acts 2:38 Acts 2:38Then Peter said to them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and you shall receive the gift of the Holy Ghost.
American King James Version×; Acts 8:14-18; 2 Timothy 1:6 2 Timothy 1:6Why I put you in remembrance that you stir up the gift of God, which is in you by the putting on of my hands.
American King James Version×; Hebrews 6:1-2 Hebrews 6:1-2 [1] Therefore leaving the principles of the doctrine of Christ, let us go on to perfection; not laying again the foundation of repentance from dead works, and of faith toward God, [2] Of the doctrine of baptisms, and of laying on of hands, and of resurrection of the dead, and of eternal judgment.
American King James Version×). It is through the indwelling Holy Spirit that Christ lives within the Christian (John 14:16-17 John 14:16-17 [16] And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever; [17] Even the Spirit of truth; whom the world cannot receive, because it sees him not, neither knows him: but you know him; for he dwells with you, and shall be in you.
American King James Version×, 23; Galatians 2:20 Galatians 2:20I am crucified with Christ: nevertheless I live; yet not I, but Christ lives in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
American King James Version×). And through this process, the believer is placed into the spiritual Body of Christ (1 Corinthians 12:12-13 1 Corinthians 12:12-13 [12] For as the body is one, and has many members, and all the members of that one body, being many, are one body: so also is Christ. [13] For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit.
American King James Version×), bringing rejoicing in heaven (Luke 15:7 Luke 15:7I say to you, that likewise joy shall be in heaven over one sinner that repents, more than over ninety and nine just persons, which need no repentance.
American King James Version×).

Again, those who have come to repentance through the calling of God (John 6:44 John 6:44No man can come to me, except the Father which has sent me draw him: and I will raise him up at the last day.
American King James Version×) are to be baptized for the forgiveness of sins, following the example and instruction of Jesus Christ. And with the laying on of hands, they will receive the Holy Spirit, empowering them to start living a transformed life led by that Spirit.