Robbing screen fits into hive entrance part of bottom board, often leaving a small enough gap for some air flow but not for honeybee or wasp access. Entrance/exit hole located at top. Simply put robbing screen in entrance snug against the box, and screw in to the brood box to secure.
Front mesh screen confuses wasps. If they do find the top hole, wasps have to slowly climb down; this gives guard bees time to prepare and intercept.