Mormons believe in the Godhead.  The Godhead is made up of God the father, his son Jesus Christ, and the Holy Ghost.  The Prophet Joseph Smith said, "The Father has a body of flesh and bones as tangible as man’s; the Son also; but the Holy Ghost has not a body of flesh and bones, but is a personage of Spirit. Were it not so, the Holy Ghost could not dwell in us" (Doctrine and Covenants 130:22).   

The role of the Holy Ghost in our lives is to bear witness of Jesus Christ and help us feel his presence on a daily basis.  He can help us feel peace.  The Holy Ghost helps purify our souls and helps us remember the covenants we have made to our Heavenly Father.  Mormons believe that the Holy Ghost confirms truth.

The gift to the Holy Ghost is received after one has been baptized and confirmed a member of the church.  After these ordinances are performed, the person is guaranteed the constant companionship of the Holy Ghost.  The spirit of the Holy Ghost can still be felt by those who have not entered into baptism but will not have His constant companionship.

When Jesus Christ came to the earth, His power and truth were evident to all who witnessed Him. When He left, He reminded the saints that He would leave the Holy Ghost with them to comfort and testify to them.

If you are trying to figure out if the Mormon Church is the true church, pray sincerely to Heavenly Father.  The feeling of peace and truth is the spirit of the Holy Ghost confirming that the things you are feeling are true. We find in the scriptures, "If any of you lack wisdom, let him ask of God, that giveth to all men liberally, and upbraideth not; and it shall be given him" (James 1:5). Moroni 10:5 states, "And by the power of the Holy Ghost ye may know the truth of all things.

The companionship of the Holy Ghost can bring great peace and comfort into your life.