Spells
Spells are the specific invocations of magic to carry out an effect; everything from heating up dinner without a fire to turning a dragon into a pig.
Any character capable of casting spells is free to learn new spells as he or she sees fit. In game terms, a character must learn the spell either from experimentation, a mentor, or a set of detailed instructions, therefore your GM should have the final approval for whether your character can learn a given spell. For instance, the availability of spells could be limited to a geographical area, and if your character from the burning desert wants to learn how to summon ice cubes for frozen cocktails, it's likely he'll have to travel to a place where the spell is common.
All spells have a target: another creature or group of creatures, an area, an object, or oneself. Spells that are cast on other creatures which cause negative effects usually require an offensive roll from you and a defensive roll from the target. Spells that a mage can cast on him or her self automatically succeed — no dice roll is required. Also, beneficial spells that a mage can cast on another creature automatically succeed (unless of course, the creature doesn't want the benefit of the spell, then a roll is required as usual).