This is a simple plate, installed OVER a light switch (not replacing the plate) which protects switches from being accidentally switched. This is particularly useful if you have a row of switches, and one is something you don't want accidentally switched on or off (like a garbage disposal).
Simply remove the screws above and below the switch you want to protect, put this plate over it, and put the screws back in place.
This will make deliberate switching easy, but accidental switching very difficult.