How did people know there was a God, long before the Bible?

Good morning, I have a question about Christianity and the Old Testament.

How did people at that time know there was a God? Before the Bible as we know it today, how did this idea appear?

Would God have revealed himself directly to certain people, or does the belief come more from traditions, stories transmitted orally or personal experiences?

Above all, I am trying to understand how this faith began. Thank you for your answers.