When Jesus ascended up to heaven after His resurrection from the grave, He promised that the Father will send us a Comforter who will be with us and lead us in to all truths. Comforter is not the only name given to the Holy Spirit. Jesus had spoken about the Holy Spirit many times during His life on the earth.
And I will ask the Father, and he will give you another advocate to help you and be with you forever - the Spirit of truth. John 14:16-17
When the Advocate comes, whom I will send to you from the Father—the Spirit of truth who goes out from the Father—He will testify about me. John 15:26
Holy Spirit is the third person in the God head Trinity. He was from the beginning even before the world was formed by the Word of God. He is not a power or force that enables you to do ministry for Jesus. He is a person with whom you can have friendship, fellowship and communion.