Magic comes in various forms. A common trait is the use of mana and some form of preparation such as an incantation, glyph, catalyst or some other pattern/item.
Mana consumes your sanity, as such extremely powerful spellcasters tend to be insane. Excessive spell casting causes aneurysms and permanent brain damage. Player characters are limited by their mana pool affected by the stat 'Intelligence'
Magic in all forms follow their own logic. The more powerful the spell the less normal logic you contain - you cannot believe magic doesn't exist and cast spells. You will still be affected by spell casting (i.e. a spellcaster creates a portal for a non-believer but they can still enter it.)
Natural talent in manipulating mana but without discipline or form. Highly dangerous and powerful with often side effects of the original intent (example: attempting to cast a fireball-like projectile spell is more likely to result in an arcane explosion with minimal range)