Theology is thinking about God and everything else in relation to God. Apart from the existence of God and his knowledge, we could not think of God at all. Apart from the existence of God and his knowledge, we could not think of anything else at all either, whether the creation around us, the world, or ourselves. See An Informal Introduction to Covenantal Apologetics.
God exists as a self-revealing God. God reveals himself to us in many ways. The ways in which God reveals himself to us will be discussed later in this work. At this point in the work it will suffice to understand that God reveals himself primarily and most clearly through the Scriptures.