The universe I created has always been my refuge from reality. As you probably notice in my works, my worldbuilding disease is pretty advanced and, I'm afraid, incurable. I'm trying to limit infodumps in the stories themselves, but if something is unclear or you simply want to learn more, I will give you more detailed explanation here.
In the future I'll also try to provide more detailed information about major worlds and cultures from my novels. But for now, here are some basics.
The Great Sphere
The universe is shaped like a sphere, spinning around Vhalfr, the only star. Unlike our stars, the Vhalfr burns with two kinds of fire: one that is hot and pretty similar to the fire on Earth; the other is cold, magical and unlike anything we have here. The whole spin-usually called the cycle-takes around two Earthy years.
On the two poles of the Sphere open two abysses, seething with raw magic: Auua and Koa. Auua is sometimes called The Lower Abyss and Koa—The Upper Abyss. The saturation of magical energy near them is so high, that the matter around is unstable: it shifts and ripples constantly. Therefore there can be no habitable worlds. Between the abysses, the Sphere is divided into Nine Circles: First is considered the bottom of the Sphere, Ninth – it's top. First and Ninth circle are completely uninhabitable. In Second and Eight there are worlds and some powerful sorcerers can survive for a short time. Third and Seventh house first habitable worlds, but the wild magic makes them bizarre and hard to comprehend for most mortals. Fourth and Sixth are pretty tolerable, but the Fifth one is the most stable and therefore serves as the heart of most of the mortal civilizations.
The Sphere itself is mostly made up of unshaped pre-matter, but sometimes the pre-matter organizes and forms bubbles. Inside those bubbles form worlds.
Now while passing through the walls of said bubbles, the matter takes form, turns into elements like we know (and many we don't): water, rocks, metals, gases. Centrifugal force pushes most of said matter toward the exterior of the Great Sphere, forming the bases of worlds. The upper parts—sky-domes—are usually clear and opened to the light of Vhalfr. Some are completely transparent, but the worlds beneath them are too hot to be habitable. For the world to be habitable, it needs an opaque sky with windows—suns, penetrable to hot fire and moons, penetrable to magical fire. Some are always open, other open and close, creating cycles similar to Earthly night and day. Some worlds don't have suns and moons, but their sky are only translucent, meaning they only let in enough light and heat to be habitable. The sky-domes have different colors (sometimes more than one) and suns and moons have different shapes: some are round or slit-shaped, other can have geometric shapes.
Of course, there are always exceptions: Mornia has completely opaque sky that no light can penetrate, while Niun has a completely transparent, although heat-blocking sky, that allows people to live beneath it, but also witness the pre-matter of The Outside in all of its glory. Sereza has no sky at all, it's completely filled with rock, with only caverns and tunnels that allow habitation, while Daesi is completely filled with water. The sky of Hara Dwett is not a dome, but a polyhedron made of innumerable hexagons, with one of them always playing the role of the sun and the other—the moon. Kuan'ta has a semi-transparent sky-dome through which you can sometimes see the silhouettes of a neighboring worlds.
Having flat worlds have some serious ramifications. Firstly, the climate within worlds is pretty uniform: it may be a bit hotter directly beneath the sun, but there are no climate zones as we know them. Secondly, the matter always flows into the worlds in shape of rain, rocks or gases. So yes, it's possible to have a world with no green plants and breathable atmosphere. And yes, meteor rains are pretty frequent in some worlds. Thirdly, there are no seasons as we know it. The opening times or sizes of suns and moons may create cycles with varying amounts of light, heat and magic, but they don't correspond to Earthly seasons. Bah, they don't even have to correspond to Great Sphere's cycles!
Fourthly, with varied (or non-existing) movement of suns and no magnetosphere, telling the directions is much different. There are two ways to do that: first, more primitive, is picking up a few significant landmarks (and with flat worlds, there’s no horizon to limit the visibility—you can see all the way, from edge to edge, millions of kilometers in some cases. Imagine the views!) and go from there. Second way requires some use of magic and consists of examining the natural flow of magical energy to determine one’s positioning within the Great Sphere. This way allows to discern four main directions: auua, koa, rotary and anti-rotary.
There is one more thing that needs to be said about the Great Sphere. It's not actually a sphere: it's a hypersphere. It exists in four dimensions, even though the bubbles of worlds only exist in three. That allows the existences of merges: points that take up different space in three-dimensional worlds, but one in four-dimensional sphere. Merges allow the free movement between the worlds.