Atheists claim that nature is all that exists. If nature made us, then what made nature? After all, the scientific evidence tells us physical reality had a beginning. Things which begin to exist need a cause, so nature needs a cause. That cause must be supernatural (beyond nature) by definition. God is what made nature.
But if God made nature, what made God? Nothing. Unlike nature, God is eternal. Things that are eternal never begin to exist, so they do not need a cause. How do we know God is eternal? Time is a feature of the physical world, so it began to exist when nature began to exist. That which brings time into existence cannot itself be temporal, but must be eternal. God is eternal. Nature is not. That’s why nature needs a cause but God does not.