Hi atheists, how do you define existence?

existtence (spelt with two t's) is not a word. ;-) Most animals are self-aware beings therefore existence is the awareness of one's presence in a physical and metaphysical/emotional sense.

If you want to do the Scientology version, you are a thetan (spirit) captured in a meat body.

God is a fully man-made concept. The bible is simply a collection of heavily edited historical accounts that cannot be proven to be true.