Willpower is just that. Your ability to force yourself to do something. Force of Will has always been a trait praised in tales of ancient heroes, and in this game, Willpower is very important. It can be used up, spent and regained. Your permanent rating stays constant, while you spend willpower points from your pool. If your 'current' pool ever reaches zero, your character is exhausted and doesn't give a rat's ass about the world around him. He doesn't care anymore. 1 - Weak-willed. 2 - Timid. 3 - Unsure. 4 - Questionable. 5 - Definite. 6 - Confident. 7 - Powerful. 8 - Single-minded dedication. 9 - A piece of iron. 10 - Unbendable, immutable.
Others may use your Willpower as a target number for certain powers. Mages use their permanent rating. You can spend a willpower point to gain an automatic success, but you cannot spend more than one point per turn. This point must be spent before rolling. (Exception: Mages can spend willpower after an Arete roll to avoid a botch.)