Curious on learning more about the “creators” or original beings or whatever they are called.

Forgive me for my lack of proper nouns as I don’t really know anything of what I’m talking about. I keep coming across posts about “war in heaven” “old gods” C’tans, the creators, other things I can’t quite remember. Basically the reason for the existence/powers and the hierarchy of beings in 40k. Is there one original god, or multiple gods? Did they create the chaos gods? Do they still exist?

I’m curious about the origins of species in 40k, ie Necrons/Orks/Eldar/Humans. From what I’ve gathered there are several different explanations/stories.

Every sci-fi universe has something like this, but I want to know the best summary. It feels to me a little bit like WoW lore in this regard so I want to know how similar/far off it really is.