Using my philosophy of showing the "after" first, here's the final result:
from this original
....adding a little window light to the background. Here's how:
First, make a basic rectangular selection with the Marquee tool.
Next we need to make "copies" of the selection to build our window. Press Q to enter Quick Mask mode
and then make a Marquee selection around the clear (non-colored) rectangle.
Holding down Command and Option (PC: Ctrl and Alt) drag a copy of the rectangle to the right.
Then make a selection around the 2 rectangles and use the same method to make a copy below, as shown here
Press Q to return to Regular mode. Add a new layer and fill the selection with white. Apply a slight Gaussian Blur (amount will vary with the resolution of the photo)
Press Command-T (PC: Ctrl-T) for Free Transform. Rotate the rectangle slightly. then hold down Command Option Shift (PC: Ctrl Alt Shift) and drag the top handles to create some perspective.
Hide the "window" layer and make a selection of the background. In this case I used the Magic Wand.
Show the window layer and click on the Add a mask button to add a layer mask. Click on the link symbol between the layer and mask to unlink them so you can re-position the window but keep the mask in place.
To complete the effect, slightly lower the opacity of the layer