Start with folding the cardstock in half vertically then horizontally to create four squares. (Dotted lines show crease lines.) Fold in the four corners to the center of the cardstock. Crease well.

The folding pattern, known as the Miura-ori, is a periodic way to tile the plane using the simplest mountain-valley fold in origami. It was used as a decorative item in clothing at least as long ago ...