Once you have accepted the missionaries’ invitation to be baptized and become a member of The Church of Jesus Christ of Latter-day Saints, you can begin to prepare yourself spiritually for your baptismal service.  Mormons practice baptism by immersion for the remission (or removal) of sins.  Baptism is a symbol of your covenant, or promise, with Jesus that you will take His name upon you and keep His commandments in return for which, He will forgive you of your sins and bring you back to live in Heaven with Him. 

A Book of Mormon prophet named Alma taught us about what baptism means. 

Behold, here are the waters of Mormon (for thus were they called) and now, as ye are desirous to come into the fold of God, and to be called his people, and are willing to bear one another's burdens, that they may be light;  Yea, and are willing to mourn with those that mourn; yea, and comfort those that stand in need of comfort, and to stand as witnesses of God at all times and in all things, and in all places that ye may be in, even until death, that ye may be redeemed of God, and be numbered with those of the first resurrection, that ye may have eternal life-- Now I say unto you, if this be the desire of your hearts, what have you against being baptized in the name of the Lord, as a witness before him that ye have entered into a covenant with him, that ye will serve him and keep his commandments, that he may pour out his Spirit more abundantly upon you? (Mosiah 18:8-10, pg 181)