Only sorcerers and Half-Bloods can use magic
Magic can only be used in the human form
Using too much causes tiredness, unconsciousness and sometimes death
Magic is drawn from someone's magical presence.
A Crastian band can restrict magic (it injects a poison into the blood that shuts off the part of the brain connected to someone's magical presence)
A mage is the opposite of a sorcerer, they have no magical presence of their own (all living things besides mages have a magical presence) and so
they can absorb magic from sorcerers and Half-Bloods. This causes pain and in severe cases death to the magic user
Humans cannot use magic
You can create your own spells but it is extremely dangerous