So you've brought a spell caster along. Wonderful! Let's cast some spells.
Clerics and wizards are helpful supporters to a party. First, let's choose the elements these guys will study. Note: Each spell caster can only be assigned one element for the entirety of the game, though more than element may be represented in your party. Think of it like having an area of focus.
For example:
For our Cleric, we want to be able to heal our party. For our wizard, we want to add as much pain to the enemies as possible. So let's choose the Earth element for the Cleric and the Fire element for the Wizard.
(see attachment for list of spells)
You'll notice that every spell has a power value stated, and that some have two power values. These are the amount of successful MANA dice rolls you will need to perform a spell. Clerics can only choose between the Earth and Light elements, whereas a Wizard may choose any element. Because Clerics only have two options, they find that they are more proficient in them, and have a lower power value than a wizard, who probably more enjoys blowing things up.
Now, from your chosen element, choose ONE spell to start with. I'll choose Embrace and Fireball for our Cleric and Wizard respectively. Why only one? Because gaining extra spells later will be a challenge in the game! Duh! Also, every spell caster may attempt to cast as many spells as the number of spells they know. If, for example, our Cleric knew all four Light spells, he could attempt any of them four times, even if that meant casting one spell four times in one round!
Note: Though I see no reason to make a hard rule here, you will probably find it easier to perform all your skills first, and then perform your spells.
So back to our previous battle:
The Gretchins are weak and scared. We came out ok. We already know we get to throw out some extra DEF dice, so let's risk some magic!
Our Cleric (we'll call him Derrick) will attempt to cast Embrace to heal up our party a bit. Now here's the benefit of having a party MANA pool. Even though the Cleric's base MANA stat is 2, he can use as many MANA dice as he pleases to cast his desired spell. Careful though: if you ever make a MANA roll where all dice come up as 3 or lower, your party suffers a -3 HP hit, with no chance to defend against it. Imagine that so,etching goes horribly wrong with the spell and it backfires. With really neat explosions and such.
So we'll roll 3 dice for Derrick as he attempts to heal our party:
4, 4, and 4! Excellent!
Scratch off that lost HP and someone get Derrick a Snickers!
Now it's our Wizard's turn. For political correctness, we'll make her a girl. And nothing rhymes with wizard so we'll name her Kathy.
We'll also roll 3 MANA dice for this attempt at casting Fireball, simply because it's our last spell this round and that's all that remains in our MANA dice pool!
3, 4, and 6! Man Kathy is one Fire (the jokes get worse from here on out).
So without even needing our extra DEF dice, what remains of the Gretchins lies in a smoldering pile of ash.
Awesome.