I was a little worried, since I have lattice on my lower screens, but I removed the lattice and screen, used the door frame as a stencil, and cut the hole around it in the lattice. Then I installed the door as instructed. There are about 3(?) steps. Super easy! You pretty much screw the door frame onto your screen, cut the screen out, inside the door, and hang the door.
My tall, 25 lb dog got it, immediately. It is a gentle enough closure for my 6lb and 10 lb cats to work, too - though they ref...