Cosmology and Ontology in Your World

Basically what philosophy do you assume for the metaphysics (or lack thereof) of how the world works? Is there only one universe? Multiple timelines? A Multiverse? How is it constructed? Is the universe Deterministic or Random, are their consistent laws or is the world bent by anthropomorphic principles (will of gods or other beings) What is the nature of what consciousness or what it means to be human or sentient. Is there a hierarchy? Is your world explicitly metaphysical or materialistic?

And how much does any of this play into the actual events of the story either directly with in-universe mechanics or indirectly with how your character's perceive and act on the world? If you know the nature of your world's Cosmology and Ontology do your inhabitants know? If so, how do they know? If not, what are the nature of their existential debates and beliefs?