He revealed himself through his creation. Whether you believe in revelations or not, you cannot deny his existence. Look above, look around and look at yourself and ponder his sophisticated creation. He is the greatest scientist, engineer, mathematician and artist.
He is indeed one; he contains everything, and nothing contains him. He is light upon light.
You don’t have to belong to an institutional religion to know him. He created everyone and everything, and he listens to everyone and everything. talk to him your own way.