It was Dill's last night in town, so Jem and Scout went over to visit with him. Jem and Dill had already decided that they were going to go to the Radley house and see if they could get a look at Bo Radley. The passage you mention starts as they are entering the Radley property. The house is described, and it is obviously in bad need of repair. Instead of a column to support the roof of the porch, it has a 2 by 4 piece of wood, which is a very weak substitute. An old Franklin stove, which is one that provides heat during the winter -- many of them were potbellied, is in the corner of the porch with a mirror above it. As they enter the gate, Jem steps on some chicken droppings and groans. The children creep to the side of the house around to a window that has a hanging shutter. The window was several inches above Jem's head. Dill was the smallest of them, so Jem and Scout make a cradle with their arms and hands and boost Dill up for a glance inside. Dill only sees curtains. Jem suggests that they go around the back, and Dill suggests they try the back window. Scout is afraid and protests. Jem starts up the first step and it creaks. He stops and waits. He then skips the next two steps and heaves himself onto the porch. He has to regain his balance but then makes his way to the back window and looks inside.
Just then Scout sees a shadow of a man with a hat on. At first she thought it was a tree, but trees don't walk. The shadow moves toward Jem. Then Dill sees the shadow and puts his hands to his face, coveringing his eyes. Jem sees the shadow when it gets close to him. He puts his arms over his head to protect himself and stiffens, waiting for what is going to happen next. The shadow stops , his arm comes out from its side, drops, and goes still. The shadow then leaves by going over to the side of the house.
Scared and relieved, Jem jumps off the porch and scoots Dill and Scout through the gate, hiding them in the collards or garden. Scout tripped on some of the plants. As she is lying there, she hears a gunshot coming from the house that can be heard in the neighborhood. Dill and Jem jump beside her. Scared, Jem tells Scout to get to the fence by the schoolyard.
When they get there, Jem holds the wire on the bottom of the fence so that Dill and Scout can crawl through to safety. But when he tries to get through, his pants get stuck on the fence. He has to take his pants off to get to safety.