There are three separate persons in the Godhead: God, the Eternal Father; his Son, Jesus Christ; and the Holy Ghost. We believe in each of them (A of F 1:1). From latter-day revelation we learn that the Father and the Son have tangible bodies of flesh and bone and that the Holy Ghost is a personage of spirit, without flesh and bone (D&C 130:22–23). These three persons are one in perfect unity and harmony of purpose and doctrine (John 17:21–23; 2 Ne. 31:21; 3 Ne. 11:27, 36).
God the Father
It is generally the Father, or Elohim, who is referred to by the title God. He is called the Father because he is the father of our spirits (Mal. 2:10; Num. 16:22; 27:16; Matt. 6:9; Eph. 4:6; Heb. 12:9). God the Father is the supreme ruler of the universe. He is all powerful (Gen. 18:14; Alma 26:35; D&C 19:1–3), all knowing (Matt. 6:8; 2 Ne. 2:24), and everywhere present through his Spirit (Ps. 139:7–12; D&C 88:7–13, 41). Mankind has a special relationship to God that sets man apart from all other created things: men and women are God’s spirit children (Ps. 82:6; 1 Jn. 3:1–3; D&C 20:17–18). There are few recorded instances of God the Father appearing to or speaking to man. The scriptures say that he spoke to Adam and Eve (Moses 4:14–31) and introduced Jesus Christ on several occasions (Matt. 3:17; 17:5; John 12:28–29; 3 Ne. 11:3–7). He appeared to Stephen (Acts 7:55–56) and Joseph Smith (JS—H 1:17). Later he appeared to both Joseph Smith and Sidney Rigdon (D&C 76:20, 23). To those who love God and purify themselves before him, God sometimes grants the privilege of seeing and knowing for themselves that he is God (Matt. 5:8; 3 Ne. 12:8; D&C 76:116–118; 93:1).
God the Son
The God known as Jehovah is the Son, Jesus Christ (Isa. 12:2; 43:11; 49:26; 1 Cor. 10:1–4; 1 Tim. 1:1; Rev. 1:8; 2 Ne. 22:2). Jesus works under the direction of the Father and is in complete harmony with him. All mankind are his brothers and sisters, for he is the eldest of the spirit children of Elohim. Some scripture references refer to him by the word God. For example, the scripture says that “God created the heaven and the earth” (Gen. 1:1), but it was actually Jesus who was the Creator under the direction of God the Father (John 1:1–3, 10, 14; Heb. 1:1–2).
God the Holy Ghost
The Holy Ghost is also a God and is called the Holy Spirit, the Spirit, and the Spirit of God, among other similar names and titles. With the aid of the Holy Ghost, man can know the will of God the Father and know that Jesus is the Christ (1 Cor. 12:3).
For more scriptural references, see: lds.org