This is first in a line the single target, extra damage combat commands (1-8) for the Commando profession. It can only be performed while a ranged, non heavy-weapon is equipped. You get your first focus fire (focus fire 1) at level 1. You get your last (focus fire 8) at level 90. The entire Focus Fire line, including most other, or all, of the commando special abilites require, as said, a ranged, non-heavy weapon (free targeting), and also can't be used with any melee weapons, i.e., swords, daggers, axes.