The assumption that you are making is that there was a point in time when absolutely nothing existed, be it physical or spiritual. But if you think about it, it would be very strange for their to be nothing and then suddenly something is there. So in that sense, you’re question is very sensible. You have actually cut right to the heart of all theories of ‘beginnings’ that don’t include God.
The simple answer to your question is that God always had and always will exist. We call him a"Supreme Being” because he is ‘higher’ than other beings. God is the eternal creator and everything else, like you and me are created by him. The Bible describes Jesus as the"author of life” (Acts 3:15) and says that God created the universe"through him” (Colossians 1:16).
So God was never made, he always was and is and will be. Our minds can’t contemplate this fact, that God is before all things, in the same way that they can’t contemplate complete nothingness.
To look at this more I suggest that you get your hands on a bible and read these passages: