Alright, so here's all the different types of magic and how they work. I may or may not retcon this. All magic can be used in a good or evil way.
Evocation or conjuring is one of the most popular magic types. It's powered by how holy or unholy the user is, and where his/her favour with the gods are. It can be used to create things such as blades of light, holy fire or weapons made of shadow. At it's most powerful, it can be used to summon demons, gods and inhuman spirits. At it's weakest it can be used to cause illusions, charms and curses. It can also be used for healing, enhancement and excorcisms.
Alchemy is basically magical chemistry. It is much more popular with dark magicians because it can theoretically cause immortality, create living dolls and change common metals into gold. The alchemic process involves mixing chemicals mostly, but there's also the ability to tie souls into physical objects (a very difficult task, but not impossible. The darkest ability alchemists have is creating life, either by combining animals or by creating their own. Both take and incredible amount of skill though, as the animals usually die quickly. Some alchemists have combined men with animals, or bred demons with men. Alchemists are also known to value personal perfection and science over everything else.
Necromancy involves speaking with the dead mostly, but there have been tales of a great necromancer who would summon revenants, soulless bodies who did as their master commanded until they fell apart entirely. Communication with the dead involves scrying, which is viewing the afterlife (or the living world) through a reflective surface. Speaking with the dead can allow the necromancer to tell the future or learn more about the past and present, since the world of the dead isn't bound by time.
Shifting is the power to change one's form. This can be done through alchemy or conjuring. It can also be done by some creatures like the succubus/incubus.