Dome Tent

Yes, the bottom screen goes behind the tire.  You'll have to make a vertical cut to fit it around the axle.  As far as the step, your instinct probably says to make a horizontal cut - don't - instead, make two vertical cuts, one at either side of the step that goes as high as the step.  That way, you'll have a piece of screen which slides behind the step.

We've never used the screen, but others here have cut it like you said.  There are plastic tabs that screw into the pod that match up with the metal rings but I don't suggest using them.  Ours have always been a huge pain (hard to snap on/off, and some don't hold well) and I've seen other methods tried successfully such as suction cups.