Baptism is the first of the "saving ordinances" (those ordinances required for salvation). It is the ordinance by which we take upon us the name of Christ and promise to obey God's commandments. It is the ordinance by which we become members of the Church. It is also the ordinance by which we signify our repentance of our previous sins and by which they are washed away through the atonement of Christ. As such, a person must be mature enough to have an awareness of the difference between good and evil and be capable of repentance. Because of this, we don't baptize people until they have reached at least the age of eight years old. We don't consider children younger than this to be accountable for their actions. The manner of baptism is laid out in the Doctrine and Covenants (a book of modern revelations, most of which were given to Joseph Smith). We believe in baptism by complete immersion. A male who holds at least the office of Priest goes down into the water with the person to be baptized until the water is somewhat over waist deep. Then standing somewhat behind the person, the Priest calls him or her by their full name and then says, "Having been commissioned of Jesus Christ, I baptize you in the name of the Father, and of the Son, and of the Holy Ghost. Amen." Then the person is lowered backwards into the water until they are completely submerged and then brought back up again (http://scriptures.lds.org/dc/20/72-74). There is a twofold symbolism involved in this ordinance. First of all, it should remind us of the death, burial, and resurrection of the Savior. It is also symbolic of the end of our old lives and our rebirth as followers of Christ and members of the Church.