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The defense roll for armor is the same as any other roll: 3d6, take the middle die, add a relevant bonus, and succeed on a 5 or more (or another number if the GM decides it should be higher or lower). The defend action is an action that blocks damage by parrying, dodging, etc. 

Armor works like the defend action, but it doesn't count as one of your actions. You can still add a bonus if you have one that is relevant to using armor. A "wizened sage who brews potions" would just roll the bones and hope for the best, but a "brave knight who slays dragons" would add the +2 bonus for being a knight: he knows how to roll with the blow and tuck his arms in (to avoid exposing the less armored spots like the inner elbow and armpit) to get the best use out of his armor. 

Regarding "exploits" versus "experiences": it's mostly a branding thing. The word "experience" has been an abstract number in games (both tabletop and video games) for several decades now. It's the default understanding of "experience". It really needs a different name to avoid confusion, just like games that require you to spend points to attack call them "action points" or instead of "hit points".