Do you mean as in dodging? If that's the case, you need to be a Journeyman in Acrobatics before you gain the option of dodging. After that, it's simple. To do a quick dodge in combat, hold block and then tap the movement stick/button for the direction you want to dodge in.
I've never pushed a character to that level of Acrobatics, however, so I've never seen it in action, but I've read the booklet from the game.