As far as mortals know with reasonable certainty, there are only two planes--the Material Plane, where pretty much everything recognizable resides, and the Void. Various religions and mythologies make mention of other worlds--heaven, paradise and the like--but if other planes exist in the multiverse, they cannot be reached or contacted by any means known currently.
The Material Plane is pretty standard fare. It includes the planet of Arendia upon which mortals and fey live, the sun that it orbits, the six moons that orbit it, and possibly other stars and planets unknown to mortals. The Void is a bit like a mix between the Ethereal plane, the Astral plane, and the Far Realm. Rather than the matter and energy found on the Material Plane, the Void is a realm occupied by Dark Energy. Exactly what Dark Energy is is something of a mystery, even to those few who study such matters in secret, but it is known that arcane spellcasters draw their powers from Dark Energy pulled from the Void, transforming it into the positive and negative energy and various forms of matter that their spells rely on using Words of Power. It is this connection to the Void that earns mages their unpleasant reputation throughout Arendia, for the Void is not uninhabited--it is home to the horrific, insane alien monsters known alternately as the Others, the Outsiders, or by other names as varied as they are themselves (think of Cthulu, the Great Old Ones, or any of the regular aberrant monsters from D&D). While arcane magic does not necessarily require communication with the Outsiders, the manipulation of Dark Energy draws their attention and entices them to interfere on the Material Plane, with disastrous consequences. Even worse, some mages actively court the attentions of these entities in attempts to increase their powers, making dangerous pacts with them and even summoning them directly into Arendia on purpose. Not all practitioners of arcane magic follow this path, but those who do have caused some of the greatest disasters in history, with the result that most common folk hold an attitude of deep suspicion and fear towards the arcane arts.
The Gods and Divine Magic
Arendia is orbited by six moons, each roughly the same size and orbiting at close to the same distance. The moons are far more than dead lumps of space rock, however--each corresponds directly to one of the six gods of Shadelight. Their movements across the sky and the patterns they form in relation to each other play a significant role in determining the course of Arendia's history and the destinies of individual mortals.
It is unclear exactly where the gods themselves reside cosmologically. Some cultures believe that the moons are the homes of the gods, others that they actually are the gods; some say the moons are windows into the planes the gods inhabit, still others that the moons really are simply objects, created by the gods and placed in the sky so mortals could mark the passing of months and years. Regardless of where the gods actually are, they do not communicate with their mortal followers directly. The fey are fond of claiming that the gods do speak to them--they group themselves based on which god they claim to descend from, and see it as their role to impart the will of their god to mortals of like mind. Whether or not this is truly the case is the subject of much debate among mortals. Many theologians believe that it is this relationship with the fey that is the source of Arendia's religious diversity--through the fey and their divine magic, mortals are aware of the gods' existence, but even among fey who claim descent from the same god, there is much inconsistency in their description of their divine heritor. One particular fey dedicated to Kane, the god of war, might describe him as an honorable and just warrior who protects and cares for his faithful, while another claims him to be a vicious predator who must be regularly appeased to avoid disaster.
Divine magic does not come from direct interaction with the gods themselves, but rather with their fey intermediaries. Divine casters gain their powers from contracts made with particular fey entities--their spells are actually the means by which they call upon their fey patron, or one of their servants, to aid them in particular tasks. A cleric casting a Cure Wounds spell is merely praying to her fey patron to use their divine powers to heal a comrade, or to send a weaker subordinate faerie to do it on their behalf. Because a particular faerie will only work for a follower a limited number of times (after all, they have many other things they'd rather be doing), divine casters are limited in the number of spells they can call upon every day. Divine scrolls represent written contracts with a fey patron to perform specific tasks at a later time outside the user's normal spell allotment. While arcane magical ability must be either inherited at birth or learned through long study, divine magic is as simple as proving one's devotion to a fey who can grant the necessary powers, and as such, divine magic is far more common than arcane across most of Arendia. Its derivation from the fey and the gods allows its practitioners to operate with much more freedom than arcane casters. On the other hand, a divine caster who displeases their fey patron might find that patron's willingness to perform magic on their behalf suddenly lost in the middle of battle.