Scripture is the living Word of the Living God. So the Bible is God's word to us, where God calls us to know Him and live forever. The reason we believe the Bible is because we believe in God and know Him in Jesus Christ.
There is a two-way relationship here. We believe the Bible because of our relationship with God and we have that relationship in, through and because of Jesus Christ. Secondly, the Bible is the living word of the living Lord, so it has the power to create faith. We do not simply jump in and believe whatever is written because it is written. We believe because of the work of God. So how does it all begin?
Our encounter with God begins as God comes into our world. It is Christmas and Easter. It is Jesus being born, living, dying and rising for us. That is where our knowledge of our Triune God begins, with knowing Jesus.
John 1:18 No one has ever seen God; the only [begotten] God, who is at the Father's side, He has made Him known.
So God comes to us; and we begin learning about God as we come to Jesus and learn about Him.