God created heaven and earth. What was around before heaven and earth? Where does God come from?
In regards to the creation see:
Could there have been a gap between Genesis 1:1 and 1:2?
How old is the world?
Was there a world before Genesis?
In regards to God, the Bible simply assumes that God exists. This is because the Bible claims to be written by God. Unless you are one of those strange philosophers, if you wrote a book you wouldn't start out proving that you exist. In essence the book is the proof of your existence. The following articles discuss the nature of God:
In particular, in the last reference see the lesson titled "The Eternal God."