General

mastery books ?

yea so i have a lv 97 aranand ive played maple on and off since the addition of thief's. ive seen mastery/skill books but never thought id get high nuff 2 use 1. this guy in a pq like lv 6x said he alredy used his for the db shadow thing. so i was wondering what do they actually do? do i need a skill alredy maxed? does it give aditional dammage% and when can u use them?