Undertale armor and combined items

[SadTransHedgehogs]

For the armor, how does it work? Or, they, really? Do I just choose the item and it's activated or do I press a certain key? Does it stay on after battle?

Also, I know some items come in sets. Which ones are those? I know about the mandanna + tough glove and the tutu + ballerina slippers, but what else?

[Canadian Normandy]

almost every armor and weapon is part of a set, usually found in the same "environment" of the game, some even found on the same screen as each other.

as for equipping your armor and weapons, you simply go into the item menu outside of battle, click the item and click "use" and it equips the item if its a weapon or armor, placing the previously equipped weapon or armor back into your inventory. you can check your currently equipped items on your status screen.

[SadTransHedgehogs]

I tried that and it didn't seem to help. I tried equipping both the mandanna and the tough glove and not only did neither appear on my protagonist but it seemed to have no effect at all.