The Godhead

God the Father presides over and directs the other two.

God the son is the creator and authority over this earth and things pertaining to it. He is the Redeemer of this earth. He give immortality to all through resurrection. He gives eternal life to all those that repent and accept him daily.

God the Holy Ghost testifies of the father and the son. He testifies of all truth. He comforts. He teaches. He is differentiated as ghost or spirit because he is the only member of the Godhead who does not have a physical body.

The Holy Ghost

Elder Dallin H Oaks, The Godhead and the Plan of Salvation, General Conference April 2017

“The third member of the Godhead is the Holy Ghost, also referred to as the Holy Spirit, the Spirit of the Lord, and the Comforter. He is the member of the Godhead who is the agent of personal revelation. As a personage of spirit (see D&C 130:22), He can dwell in us and perform the essential role of communicator between the Father and the Son and the children of God on earth.”

Doctrine and Covenants 88:66
66 Behold, that which you hear is as the voice of one crying in the wilderness—in the wilderness, because you cannot see him—my voice, because my voice is Spirit; my Spirit is truth; truth abideth and hath no end; and if it be in you it shall abound.

My thoughts
{
People try to say that God is only a spirit based on what they read in John 4:24
24 God is a Spirit: and they that worship him must worship him in spirit and in truth.

DnC 88:66 seems to add a different dimension to that.  His voice is a spirit, that spirit being the Holy Ghost.

The Joseph Smith Translation also clarifies this.  His translation gives that verse as John 4:26:
26 For unto such hath God promised his Spirit. And they who worship him, must worship in spirit and in truth.
}