Protecting your valuables and taking someone else's are surprisingly similar, in practice. Those skilled in the art of security are capable of understanding various mechanisms relating to it, and use that knowledge to (almost always) get into things they shouldn't.
At Rank 1, this talent increases your chance of unlocking doors and chests, as well as disarming any traps you find (via the Scout talent). The chance of success greatly increases with Rank; Skill and Celerity also play a part, as well as the quality of your lockpick (when picking locks). To pick a lock, right click a door or chest and select the appropriate option, or Shift+Left Click it. To disarm traps, you must first search for them, but if you've found one, use Alt+Left Click.
At Rank 5, you realize you've become much more nimble than before, gaining 5% CEL growth permanently.