Click and drag to rotate the dial. Works like a real locker combination, in that you have to rotate it clockwise for the first number, rotate completely around counterclockwise for the second number, then rotate clockwise for the third. You'll hear a click when you go past the number. You'll have to restart if you go too far from the combo number or go in the wrong direction. Press space for automatic combination-ing.
:3 (I'm working on it...)