The Fundamental Bible truth about God is that He is one. There is none beside Him.
God has made Himself known to man through various means. In the Old Testament He spoke directly to righteous men, such as Noah and Abraham. He used chosen leaders like Moses and Joshua. He also guided his people through prophets, priests and kings.
His most awesome revealing of Himself came at Bethlehem, when He came to the world as the Christ Child, Jesus. Through His death, burial and resurrection He redeemed fallen man from the penalty of sin.
Today, He reveals Himself to man through His Holy Word, the Bible. God wants us to know Him through a very personal relationship. We can walk and talk with God, and live a life that pleases Him.
This link provides scriptures about the Oneness of God and the revelation of who Jesus Christ is.