It turns on your 12 volt DC to 120 volt AC power invertor.
If you do not have it on you get no output to the outlets that its on.
Probably hooked up to the TV outlet is normal but also to your refrigerator if its a residential type that run only on 120 volt AC power.
The Manuf says this:
The Prowatt SW remote provides the convenience of a simple on/off remote function to the user. It also has an automatic ignition lockout feature to shut down the inverter’s output when the vehicle’s ignition or a 12 VDC enable is not engaged. A 25’ remote cable is included with the remote panel.
You should have to locate the Invertor.
It should look like the picture I attached.
Hopefully, he did. I installed that one in my truck camper. If the light is on the inverter is on and is also drawing some idle current (100ma) maybe. Turn it off when not using the camper and the camper isn't shore powered. Will eventually kill your house batteries.