Jesus taught that we all must be Baptized by water and by the spirit. Baptism by water must be followed by baptism of the spirit. If not then it isn't complete. When we receive baptism and the gift of the Holy Ghost, then we can receive a remission of are sins and become spiritually reborn. When a person has been baptized by water, then one or two authorized priesthood holders lay their hands upon the person's head and confirm them a member of The Church of Jesus Christ of Latter Day Saints. Then they confer the gift of the Holy Ghost upon them.
We can always have the Holy Ghost with us as long we stay worthy of his presences. He will not stay in unclean places. The Holy Ghost does alot for us and here are the things he does;
1. He gives us cleansing effect.
2. Testifies of Christ and help us to know what is truth.
3. Gives us spiritual strength, also help us do what is right.
4. Comforts us during times of trials and of sorrow.
5. Warns us when there is physical and spiritual danger
6. Provides the power by wich we learn and grow.
The gift of the Holy Ghost is one of God's most precious gifts that he can give us. By the power of the Holy Ghost we can know and feel of God's love for us and direction. This gift that we can recive is a taste of eternal joy.
Without the authority of the Priesthood we wouldnt be able to have this wonderful gift. That authority is restored through the Prophet Joseph Smith and we can all enjoy this wonderful gift. For it was lost for centries but becasuse of the Restoration of the gosple we can now all have that wonderful gift of the Holy Ghost.