God is a trinity of persons: the Father, the Son, and the Holy Spirit. The Father is not the same person as the Son; the Son is not the same person as the Holy Spirit; and the Holy Spirit is not the same person as Father. They are not three gods and not three beings. They are three distinct persons; yet, they are all the one God. Each has a will, can speak, can love, etc., and these are demonstrations of personhood. They are in absolute perfect harmony consisting of one substance. They are coeternal, coequal, and copowerful. If any one of the three were removed, there would be no God
http://www.carm.org/trinity
Another Look at the Trinity
http://www.carm.org/christianity/christian-doctrine/another-look-trinity
What is the Trinity?
http://www.carm.org/what-trinity
Response to criticism of "What is the Trinity?"
http://www.carm.org/christianity/christian-doctrine/response-criticism-what-trinity
Jesus is the second person of the Trinity. He is the Word that became flesh and dwelt among us. "In the beginning was the Word, and the Word was with God, and the Word was God. 2 He was in the beginning with God... And the Word became flesh, and dwelt among us, and we beheld His glory, glory as of the only begotten from the Father, full of grace and truth," (John 1:1-2,14). Because the word was with God and was God and became flesh, we then state that Jesus has two natures: divine and human. Therefore, Christianity teaches that Jesus is both God and man at the same time. The reason that he is God in flesh is because only God can atone for our sins; we can't do it on our own because we are finite, sinful beings and we cannot please an infinitely holy God. Jesus had to be a man to be able to die for humanity. This means that Jesus took our place on the cross; that is, He took our place and suffered the wrath of God the Father. If you trust in what Christ has done, then you will be saved from the righteous judgment of God.
http://www.carm.org/jesus
The Holy Spirit is the third person in the Trinity. He is fully God. He is eternal, omniscient, omnipresent, has a will, and can speak. He is alive. He is a person. He is not particularly visible in the Bible because His ministry is to bear witness of Jesus (John 15:26).
Some cults like the Jehovah's Witnesses say that the Holy Spirit is nothing more than a force (Reasoning from the Scriptures, 1985, pp. 406-407). This is false. If the Holy Spirit were merely a force, then He could not speak (Acts 13:2); He could not be grieved (Eph. 4:30); and He would not have a will (1 Cor. 12:11).
The truth is that the Holy Spirit is a person the same as the Father and the Son are within the Trinity.
http://www.carm.org/holy-spirit