Start by lining up one of the 1' x 3' panels to the top of the frame. Using your finishing nails secure the panel to the frame. This is where the nail gun comes in handy. If you don't have one I would recommend borrowing one. Flip the frame over, the bottom is now attached. Line up the next two 1' x 3' panels and nail them into place along the frame. Finally, line up the two 1' x 4' vertical panels and nail them to the frame.