1. Remove the two screws holding on the screen from the outside.
2. Place fan where the screen was.
3. Place screen over the fan. 
4. Secure screen using screws.
5. From the inside, connect to power supply.

View from the inside.  Vent door can be closed
and locked normally with power cord disconnected.  In this picture you can see the power cord running down the wall.  A power cord extension is included with each unit.

View from the outside