There has been plenty of misconception of who the Holy Spirit is, from opinions of man as to saying he is an impersonal spirit, which is given to followers of Jesus, to some a sort of force field. The bible is clear to state that He is God; He is a person, with a mind and feelings. He is omnipresent, being at all times everywhere, He is omniscient whereby He is all knowing, He omnipotent, which is all powerful. The word tells us He is a comforter, our comforter. He is the third person of the trinity. He is fully functional as God, but He is ever present to the world working the will of God the Father and Jesus the Son. John 14:16, 26, 15:26, points out the function of the Holy Spirit, He will reveal Jesus to us.
When we are saved we receive the trinity and the Holy Spirit is in our heart continuously. When Jesus ascended he had already told the disciples in John 14, that the Father would send the Holy Spirit in his place to teach them and be with them forever. Since Jesus was going back to heaven He was to be seated on the right of His Father and could not be here to teach them any longer and therefore the Spirit of God, the Holy Spirit, would be their comforter, advisor and director from that time forward.