Magic is fairly limited and runs on a few set rules in this world. Part of the approach I took when figuring it out is that I didn't want magic to be flashy and so devastating that non-mages can't stand up to it. When a person can wipe out armies with his power, he moves beyond the realm of "character" to "deus ex machina," and stops having any real challenges except other people who are just as absurdly powerful.
So, magic involves two parts. The first part is the conjuring of a spirit of some sort. The second part is its binding.
Spirits are tiny entities that reflect certain forces and concepts. Many of them are recognizably "elemental" -- for example, one might conjure a flame spirit, a living point of heat and light. If one reaches a body soon enough after death, the departing soul can also be manipulated. These conjurations are always fairly limited to small things. You'll never find a magic-user who can call a great pillar of fire into existance, whether because no flame spirit so mighty exists or because it's beyond human capability to conjure it. No demons or angels summoned, either. Spirits are not intelligent.
The act of conjuration involves, mainly, a circle drawn or etched on a surface with certain symbols related to the type of spirit it's meant to conjure. The circle itself is in fact a bind of entrapment; binds will be explained shortly. An act of will entices the (normally invisible) spirits to the magic-user, at which point one inevitably crosses through the area of the circle and is caught within. The spirit may be freed by breaking the circle in some fashion -- metal etching is thus common for when one wishes to keep a spirit trapped permanently, while paper is the most common medium for temporary circles. Some who conjure spirits frequently actually have various circles tattooed upon their fingertips, palms, and the backs of their hands. A simple scratch of the flesh with one's own fingernail is enough to break the circle temporarily, undoing a conjuration.
Binds are more elaborate sets of symbols and arcane signs written so they flow into each other, creating a single coherent form. At a bind's center is always the conjuring circle used to trap the spirit. One or more lines connect the circle and the rest of the bind, though never crossing into the circle itself -- that would break the circle and let the spirit free. Binds put the spirit to work at some purpose. A bind holding a winter spirit might be carved into the inside wall of a closed wagon, creating a sort of refridgerated wagon. A bind holding a flame spirit can be made inside a lantern to create a permanent light, and so on. A bind on paper could be rolled up, folded, or crumpled and still work, as long as the bind itself is not torn or smudged out of shape.
Obviously, many of these uses are fairly utilitarian. They belong to home and industrial conveniences, not the stuff of myth and legend. For this very reason, the practice of magic is considered something almost vulgar, suitable more for the working classes than a gentleman or lady. For many within high society, about its only forgiveable use is in works of art, where the bind is skillfully hidden and helps create some effect -- a soft glow in the eyes of a statue, control of shadow no matter how the light otherwise falls upon a piece, the illusion of fluidity in painted water, and so on.
There's also a side to magic that many fear, of course. It is the most "impressive" use of this magic, which involves a conjuration and binding of a spirit to a corpse. One can thus create zombies in such a manner, perhaps even trapping the body's soul if one performs the conjuration swiftly enough. It is considered an absolutely vile thing to do, to use another's body and prevent it from receiving a proper burial, and to trap the soul of the being within and denying it the afterlife, oblivion, or any kind of volition. Many are the stories of ruthless lords and kings of various lands who had this done to hated enemies upon capturing them.
This form of magic is also what is adapted by Gideon in his attempts to become a lich. The obvious problems crop up with the rumors that Gideon is experimenting with necromancy, and provide some of the conflict of the story, in addition to Gideon's own internal conflicts over whether to go through with it.