You clean yourself. You spend 13% tension points on the spell. Tension Points are imaginary points of magic potential that are gained in battle whenever you attack or dodge or sometimes when you use an item. You can use tension points to do magic spells during your turn, or to do special act commands. All monsters have this feature during battle, and it's quite simple to use these tension points after or during battle. You can use any tension points you build up until your next battle with something.
Your most recent battle was the one you fought with the newly deceased bear, in which you dodged two attacks and then attacked yourself. That gained you about 35 tension points or tp. One other thing about tp is that there's a max, 100, and once you reach that level, you deal a lot more damage than you would've otherwise. Also, spells that use tp are a bit arbitrary on how much tp they use. So a basic fire spell may cost only 5 tension points, but a fire ball may cost 50 tp for some reason. You don't use fire magic that much, instead you like using magic that splits stuff in half and also using orbs.