I put this in the game forum, but sometimes getting a response there is a bit slow...

So, when it comes to keys in Enclave, is there a certain way to use them? Are they auto-use or do you have to "do" something with them?

I'm still early in the game; the bad guy just lowered the drawbridge, then drops back down into that little square room. I kill him and take the key, but then all I get is the "You need a key to open this door" message. If that's the key I need, it doesn't seem to be working, and I couldn't figure out a way to actively use it.

Move your view/focus to the keyhole until you see a hand, then right-click

(At least that's what the manual says)