You should be carrying scrolls. Give them to your Mage. On the scroll it'll show which buttons to press to cast. There are also elemental requirements. So your Mage should at least be able to do a Fireball and Poison Cloud.
Doesn't help if you didn't go Earth or Fire. I have two Spellcraft spells that I'm still trying to figure out the combinations for with good ol' fashioned "TRY EVERYTHING!"
Though it hasn't really paid off yet.