Start with one sheet of paper
Fold it in half lengthwise
Unfold it
Fold it in half widthwise
Unfold it
Fold it in half lengthwise again
Cut or tear along the center fold between the middle two panels, stopping at the crease
Unfold the paper completely
Fold it in half widthwise
Push the two ends toward each other so the cut opens into a diamond shape
Flatten the diamond into a booklet shape
Press all folds firmly
Trim edges if needed