Each class has abilities that apply these debuffs, and each class has abilities that combo with these debuffs. Each class has a set of specific CC/debuffs: Mages have Frozen and Paralyzed Rogues have Asleep and Warriors have Stunned.
If you want to use your Focus abilities more often, you'll need to learn combos. While Focus can be gained through dealing damage, it's very incremental and takes several fights to accumulate.
