Gift of the Holy Ghost
The gift of the Holy Ghost is the subject of a Mormon ritual following baptism. Also known as the baptism of fire and confirmation (similar in some ways to confirmation in Catholicism), receving the gift of the Holy Ghost is one of the rituals required for membership in the Mormon church. Mormons believe that those who have the gift of the Holy Ghost are privy to special revelation, directly from the Holy Ghost. Those without the gift can only feel the Light of Christ.
Only Mormon men, who have been initiated into the Aaronic priesthood, are authorized to perform the laying on of hands and confer the gift of the Holy Ghost.
Light of Christ
Mormons teach that people can pray to know that the Book of Mormon is true and that Joseph Smith was a prophet of God. But since people cannot have the Holy Ghost with them until after they receive the gift of the Holy Ghost, Mormons teach that all humans are under the influence of the Light of Christ. The Light of Christ is defined as the influence of God that permeates the universe, giving life and order to all things. In this manner, it is a kind of omnipotence. The Light of Christ is also assumed to prepare people for the gift of the Holy Ghost by helping them discern divine truth.