After a certain level some of my moves appear to build up something called Centering that wears off after a certain number of seconds. I think I skipped the description of this accidentally and I can't find anything online. What does Centering do and what causes it to build?
You gain stacks of Centering whenever you spend focus or kill an enemy, and it doesn't do anything on its own until you reach 30 stacks of the buff. At that point, you can trigger Zen, Transcendence, or Inspiration:
A Jedi Sentinel gains the ability to Center. When a Sentinel attacks with force, stacks of centering are added. With more centering stacking come the ability to use advanced levels of fighting stances Zen, Transcendence, and Inspiration. For example, the activation of Zen takes place with 30 stacks of Centering. The Zen activation and specific lightsaber forms add different abilities to the Jedi Sentinel. The Zen activation and the Juyo form increase the critical chance of burning melee attacks by 100% and heals the party through the burn damage on the enemies.