Step 1: Gather your materials and tools
My original fascination for working with cardboard was the way the corrugations could be reinforced by gluing two layers together at right angles. I've since learned (the hard way) that the weakest point is the folds where the box flaps are. You can see here that I've reinforced them.
The only tools I used were a tenon saw, a hammer and chisel, a file, a box-cutter knife, some big scissors and some wood glue.