Prepare the shadow box by gluing decorative paper or fabric to the background of the shadow box. Because most shadow boxes have a plain wooden backing board, the paper or fabric make the finished box more attractive.
Gather examples of the basic 3D shapes: a sphere, cone, cylinder, pyramid -- either square, rectangular, triangular or hexagonal -- and prism, either rectangular, triangular or hexagonal. For instance, use a ping pong ball, party hat, dice or small boxes. Make sure that the shapes will fit inside the shadow box.
Place the shadow box on its back. Test out different arrangements of the 3D shapes until you are satisfied that they all fit and can be seen. Some items will be attached to the backing board and others can sit on the bottom of the shadow box.
Affix the items in the box with glue. To help shapes pop off the back, first glue small squares of foam or wooden blocks to the backing board of the shadow box. Once they dry, mount the 3D shapes on them with glue.
Prepare a label for each shape with paper and markers. Cut out each label with scissors.
Finish the shadow box by gluing the labels to their respective 3D shapes.