First Article of Faith

1 We believe in God, the Eternal Father, and in His Son, Jesus Christ, and in the Holy Ghost.

What is the very first thing Joseph Smith wanted people to know about the doctrine of the Church?

Elder Perry summed it up better than I could:

"The first article anchors our belief in God, our Eternal Father, in His Son, Jesus Christ, and in the Holy Ghost. How grateful we are for a knowledge of Supreme Beings that rule and govern this world. Our belief does not come from the speculations of men about the existence and nature of God, but from firsthand experience from the Prophet Joseph Smith in the Sacred Grove. His experience clarified for mankind the existence of God the Father, God the Son, and God the Holy Ghost. Thus to the world came the vision that three personages comprise this great presiding council of the universe and have revealed themselves to mankind as three separate beings, physically distinct from each other as demonstrated by the accepted records of their divine dealings with mankind. We know the occasions where they have been in evidence to mankind as three distinct personages. It is clear that the Father is a personal being possessing a definite form of body, parts, and spiritual passions, that Jesus Christ was with the Father in spirit before coming to dwell in the flesh, and through whom worlds were made. He lived among men as a man, with all of the physical characteristics of a human being. After His Resurrection He appeared in that same form. The Holy Ghost, also called Spirit or Spirit of the Lord, Spirit of God, Comforter, or the Spirit of the Truth, is not tabernacled in a body of flesh and bones but is a personage of spirit. The Holy Ghost is a witness of the Father and of the Son declaring to man their attributes, bearing record of the other personages of the Godhead." -- Elder L. Tom Perry, April 1998 General Conference

One of the main differences between the restored Church of our Savior and a lot of other Christian religions is what we believe about the Trinity or the Godhead.

We know that Our Heavenly Father, His Son Jesus Christ, and the Holy Ghost are three separate and individual beings.  Heavenly Father and Jesus Christ having bodies of flesh and bone as tangible as ours and the Holy Ghost is a personage of Spirit.

"The Father has a body of flesh and bones as tangible as man’s; the Son also; but the Holy Ghost has not a body of flesh and bones, but is a personage of Spirit. Were it not so, the Holy Ghost could not dwell in us."  -- Doctrine and Covenants 130:22 

This simple knowledge about the Godhead is much different than most of our other Christian friends.  They simply don't have the modern-day revelation to clarify this doctrine.