My take on it
The Holy Ghost is the third member of the Godhead. He is a personage of spirit, without a body of flesh and bones. He is often referred to as the Spirit, the Holy Spirit, the Spirit of God, the Spirit of the Lord, or the Comforter.
The Holy Ghost works in perfect unity with Heavenly Father and Jesus Christ, fulfilling several roles to help us live righteously and receive the blessings of the gospel.
He “witnesses of the Father and the Son” (2 Nephi 31:18) and reveals and teaches “the truth of all things” (Moroni 10:5). We can receive a sure testimony of Heavenly Father and Jesus Christ only by the power of the Holy Ghost. His communication to our spirit carries far more certainty than any communication we can receive through our natural senses.
As we strive to stay on the path that leads to eternal life, the Holy Ghost can guide us in our decisions and protect us from physical and spiritual danger.
Through Him, we can receive gifts of the Spirit for our benefit and for the benefit of those we love and serve (see D&C 46:9-11).
He is the Comforter (John 14:26). As the soothing voice of a loving parent can quiet a crying child, the whisperings of the Spirit can calm our fears, hush the nagging worries of our life, and comfort us when we grieve. The Holy Ghost can fill us “with hope and perfect love” and “teach [us] the peaceable things of the kingdom” (Moroni 8:26; D&C 36:2).
Through His power, we are sanctified as we repent, receive the ordinances of baptism and confirmation, and remain true to our covenants (see Mosiah 5:1-6; 3 Nephi 27:20; Moses 6:64-68).
He is the Holy Spirit of Promise (see Ephesians 1:13; D&C 132:7, 18-19, 26). In this capacity, He confirms that the priesthood ordinances we have received and the covenants we have made are acceptable to God. This approval depends on our continued faithfulness.
All honest seekers of the truth can feel the influence of the Holy Ghost, leading them to Jesus Christ and His gospel. However, the fulness of the blessings given through the Holy Ghost are available only to those who receive the gift of the Holy Ghost and remain worthy.
After a person is baptized into The Church of Jesus Christ of Latter-day Saints, one or more Melchizedek Priesthood holders lay their hands on the person’s head and, in a sacred priesthood ordinance, confirm him or her a member of the Church. As part of this ordinance, called confirmation, the person is given the gift of the Holy Ghost.
The gift of the Holy Ghost is different from the influence of the Holy Ghost. Before baptism, a person can feel the influence of the Holy Ghost from time to time and through that influence can receive a testimony of the truth. After receiving the gift of the Holy Ghost, a person has the right to the constant companionship of that member of the Godhead if he or she keeps the commandments.