It takes a Will Point each turn to attack an oppenent. If you want to increase the power of your spell, then you can spend another Will Point.
Each of the spells that you cast, cost energy from your sunstone. Unless is is a Keystone (because all of the Keystones draw their power from the sun), and surrounding sunstones. Once you get down to 0/25, you are dead.
Instead of casting a spell, you also have the choice of attacking with a weapon or an item.
Once your sunstone is down to zero, it is dead and it can not be recharged. For each day in full sunlight, the sunstone will absorb 24 charges. If you ingage in combat above the veil, you can't run out of charges.
Abilities can also be used while attacking. They can help you deal more damage, or during normal times, you can use your abilities to do anything from climbing to running.