There are multiple dimensions in the kizasphere. However, most of the stuff happens in Dimension 9, home of Earth.
Whatever you do, don't confuse these with 3D, 2D, and all that fun stuff.
Dimensions are highly unique and filled with their own galaxies, planets, resources, and life forms. There are infinite universes, an overwhelming majority of them are dead and empty, most of them for their own unique reason.
All universes have an ID, which is a whole number. Their whole number can be negative, but can not have decimals.
Dimension 0 - Considered the birthplace of magic by the people who don't know much about magic. It's almost dead and empty, thanks to space-worm-things eating it.
Dimension 9 - Home of Earth, the most important dimension of them all.
Dimension 11 - "Realm of Infinite Planets", consists of one galaxy with a lot of planets.
Dimension 12 - "Everforge", created by remnants of forgotten dreams.
Dimension 57 - "Vitera", considered the most odd universe which can't be summarized easily.