Christians believe that there is only one God, but that he exists as three persons, the Father, the Son and the Holy Spirit. This doctrine of the Trinity is one of the most difficult to understand, but is central to the Christian faith.
In this video, I present evidence to show that the doctrine of the Trinity is the correct view of God, and also show why it is so important.
The transcript is here: S1V2_transcript
See also Bible Doctrine.