So back to the main questions: Who is God; who is Jesus Christ; and what is the Holy Spirit? God is our Father, who art in Heaven. Yes, our Father, who created the heaven and the earth (Genesis 1:1 KJV). Everything that ever was, ever is, and ever will be is fashioned by the hand of God. He is the one true being in existence who sees all, hears all, knows all, tells all, shows all, assists all, blesses all, and even disciplines all according to His Will, glory, and benefit.
Next, who is Jesus Christ? Jesus Christ is God made flesh, into the form of man, to come down and use His earthly created body as a sacrifice for everyone’s sins (John 3:16 KJV). These sins are for everyone that existed during his time as he walked the earth, and for future individuals like you and me, and for many, many more generations to come after us, until the end of the world.
The Holy Spirit, or Holy Ghost, is the essence of God as if He were still here as man in the flesh, Jesus Christ, giving us insight and knowledge of the truth of His word. The Holy Spirit is the soft calling-feeling we feel whenever we are called to do something good for another. And, on the contrary, it is the disapproving voice on the inside of us when we know we are not doing the right thing (Romans 8:9 KJV).