The Church’s first Article of Faith states:
“We believe in God, the Eternal Father, and in His Son, Jesus Christ, and in the Holy Ghost.”
Mormons do not believe in the traditional doctrine of the trinity precisely because that’s what it is — tradition. This doctrine was made up by men, voted on and changed over centuries of debate. Instead, Mormons believe in the Godhead — God the Father, God the Son, and God the Holy Ghost, as three distinct beings.
Why do we believe this? In the spring of 1820, a humble boy name Joseph Smith prayed in a grove of trees near his home. He was searching for truth, to know which church to join. In a remarkable experience, God the Father and His Son, Jesus Christ, appeared to Joseph Smith, calling him to be a prophet to restore the true church of Jesus Christ. Among other things, this amazing experience cleared up once and for all that the doctrine of the trinity is false, that God and Jesus are separate beings.
That experience aside, it just makes simple sense—God is not some confusing, incomprehensible being. We are His children, created in His image, and He wants us to know Him, to develop a relationship with Him. That’s hard to do when we can’t even understand confusing creeds that talk about how he is one God in three and three in one.