I was given a wrist attachment that's supposed to be a stunner of some kind. I was also told that when I come across a case when its needed I will be told, except I haven't come across that situation yet. What am I supposed to do with it?
You don't do anything with it that I found except when they tell you to and even then it is not something you active but something that is used in cinematics.
From a mechanical point of view you as a player will never need it.