God is the Alpha and Omega, the beginning and the end. God is infinite. In other words, God IS the "Originator," without Whom no thing can even exist. His existance is independent of anything else. While everything elses existance is dependant on Him. He says to Moses in Exodus 3:14, "I AM THAT I AM."
14And God said unto Moses, I AM THAT I AM: and he said, Thus shalt thou say unto the children of Israel, I AM hath sent me unto you.
I know this might sound a bit abstract, for God's ways are beyond human understanding. Only "science" to ever come close to explaining the Being that is God is with Quantum mechanics.
Another way to explain it, or rather not explain it, is that God just is.