Working with a 3d floorplan - how to layer differnet zones as off (GIMP)


So while i can code, i cant do photoshop, im litteraly like a 95yr old at a computer when i open photoshop and gimp etc.

I have a render of my 3d floor with all lights off, all lights on, then invidual rooms off. Ive tried importing them all as layers in GIMP and messing around with a lasso tool, but i cant wrap my head around what im supposed to do.

Any tips?

Explain like ur talking to a 5yr old

This is what im working with btw