The planes describe the a metaphysical relationship between the prime material plane (where reality, life, and death occur) and the beyond (thought, religion, afterlife, creation, etc.)

Key Differences with Other Cosmologies

Faewild is an extension of the Ethereal Plane. It exists on the edges of the Ethereal, where it butts up against the prime material plane. Thus, it is a hyper-realistic version of it's neighbor, had mortals not exerted their will over the land. In the Faewild, should you travel too far from where you entered, you are liable to find yourself somewhere else entirely when you return to the prime material plane

The Shadowfell borders on the nexus of the Negative Energy Plane, the Ethereal Plane, and the prime material plane.

The Prime Material Plane

The prime material plane contains all of creation. Each world is suspended inside a sphere of inert grey materials that defies comprehension. This material holds the phlogiston, an intensely combustible rainbow-hued fog that fills in void between spheres, at bay.

Thimtona and the Prime Material Plane

Thimtona, on its own, is not a world meriting any particular special considerations; although in the past, the Divine Host of Thimtona was Forbidden from the world via the intersession of Naworna. Since the Upheaval, Naworna's workings have been sundered and Thimtona's crystal sphere bobs and buoys upon the flow of the phlogiston, like many others.