Summarize the following:
Arrange the panels in this order: back, bottom, front, and flap. Make sure that the long edges are parallel to each other, and that they have about 1⁄4 inch (0.64 cm) of space between them. You'll end up with a rectangular shape. If you made the front flap pointed or rounded, position the shaped edge on the outside of your rectangle.

Summary:
Line the panels up, side by side, to create a rectangle.