Fold the paper into 8ths (folding in half lengthways, vertically and diagonally)
Fold in all four corners to the center to make a smaller square
Fold this smaller square into thirds on both axis to create lines that separate the square into 9 tiny squares.
Open up one of the corners of the smaller square, then fold in the left and right tiny squares in the top row until it brings in one of the walls of the boxes. There will be a little triangle sticking up. Tuck that in.
