Warrior skill - Counter-attack

[Gus]

Hi all,

I trained in the "War Academy" after beating a number of "sword-wielding" units, and got access to a counter-attack skill, but... I don't know what it is, how to use it, if it can be skilled up, etc.

Any help? I'm sure it's very dumb, so if you help me, I'll let you mock me =P

Thanks!

EDIT: sorry, I thought I was in the Crossworlds section, I will post again there.