Got this skill but I am not seeing any indication of how to use it. I realise it's a counter but I cannot see any flash or warning to tell me to use it? I assume you just parry and then counter? Or am I doing it wrong?

I haven't invested in the sword-tree, but per the manual, if you have that talent, your cursor icon while blocking should at some point change to a sword/weapon icon, attack then for the counter attack.

Ah ok will try it out. Thanks mate.