Torch - A simple but powerfull fire spell good for lighting torches, fireplaces, campfires, and also monsters and other enemies. It does minimal damage to living organisms and a simple stop, drop, and roll will put out any residual flames.
Fire Arrow - A stronger and farther reaching fire spell which is good for enemies who are too fast for Torch or for moving targets. Also quite handy if you're intending to burn down a village or bridge, (or if you want to film a movie).
Fireball - The strongest of the fire spells, this is a spell used almost exclusively for either combat or massive collataral damage. Weather burning down a city or starting a festive bonfire this spell will do the job quickly and with much screaming and fleeing from terrified villagers. It is also good for dealing with particularly large monsters or hordes of undead.