How to recruit captains? (Middle-earth: Shadow of War)

Fighting the caps early in the game, press B on the incidence but nothing happens, ie I can kill but can't recruit! With higher-level caps, there is triggered the finishing moves at the end when cap was exhausted, displayed key and you need time to click, but if it prozhat, Talion kills him just as if not prozhat the cap goes, and how to recruit?? Or this option will appear on the plot?