To make a cube out of six business cards, first take two cards and
place them across eachother at right angles, centering them as nearly
as possible. Fold the flaps of the bottom card down over the top
card. Turn them over and repeat. Pull the two cards apart. Six of them
can be assembled as shown above to make a cube. All flaps must be on
the outside of the finished cube.
Two cubes can be linked by positioning them as shown above. Take the
two flaps on one face and tuck them under the corners of the two flaps on
the adjacent face of the other cube. The joint is surprisingly
strong! You can keep adding cubes like this to build any structure
you can think of.
If you don't like the flaps showing on the outside of a face, you can
cover them with another card by tucking its flaps under the corners of
the flaps you want to hide.