God as part of a trinity is almost universally taught in mainstream Christianity. However this is not the teaching of the Bible. The Bible is very clear that God has always been and will always be one God and that Jesus is his son.
The Old Testament
The Old Testament is full of statements about God. It is also the basis of Judaism which has always maintained the unity of God.
The New Testament
The New Testament begins with Jesus Christ and ends with a message from him as to future events. If Jesus was God surely somewhere in these pages there would be clear teaching of this change in doctrine. Not only does this not happen but there are numerous teachings and references to God as one and to His son, Jesus.
What God is like
So how can we find out about God?
God can be known
The Bible reveals what God is like.
The picture of the unity of God is consistently written throughout the Bible, both Old and New Testaments.
That one God is identified as the Father.
We can understand this God and so come to know him.