Find a cube-like mold. You will apply a papier-mache mixture around it. Use a cubical structure that the papier-mache mixture will not permanently adhere to, such as one made of a plastic or nonporous material. Or you may use a plain cardboard box instead of a mold if you don't mind it becoming part of the papier-mache creation.
Tear cardboard and newspaper---or any other paper product---into tiny strips. Soak the strips in water until you have a pulp-like mixture. You may add flour as an additional adhesive to help the mixture hold together.
Apply the mixture to your cubical structure mold or cardboard box.
Allow the papier-mache to dry completely. This process may take several days.
Remove the dried papier-mache box from the cubical structure mold. If you used the plain cardboard box, it is ready when dry.
Paint or decorate the papier-mache box as desired.