The Sacrament of Confirmation is defined as a "mature public affirmation" of faith. (Book of Common Prayer, pg 412).
For those baptized as infants or young children, it serves to confirm the vows that were made at the baptism. For adults growing in their faith journey, Confirmation recognizes a maturing faith.
Those desiring to be confirmed must be baptized and have completed a course of instruction. Confirmation is perfomed by a Bishop with the laying on of hands.
The Bishop's visit is also a time at which those who have made a mature public affirmation of faith in other deominations may be recieved into the Episcopal Church.