Normally, the battle menu on the lower left corner of your screen consists of only the Attack, Magic and Item commands along with a ? in the 4th box. But whenever you see a field icon (?) above Sora's head, it means that a special command is available. So now, there will be a 4th option in the battle menu.
The commands are usually "Examine" for anything that has to do with advancing in the game, but with the exception of locked treasure chests. "Open" if you're standing in front of a treasure chest. The other one is "Lift" for barrels and crates.