Masteries
As you level up, you'll unlock mastery points. These are specialized bonuses that let you customize your champion's stats. Masteries are organized into three trees, and adding points to a tree unlocks increasingly powerful masteries.
Mastery Builder
Click on a mastery icon to put a point into that mastery. Right-click to remove points from a mastery.
As you put points into masteries in the same tree, you'll unlock more powerful masteries.