I don't remember where I first saw this, but it's a useful trick for making a small note-book from a single piece of paper, maybe for recording revision notes on.
Step 2: Making the basic book.
Watch the video instead...
Step 3: Extending the concept.
As long as you fold the paper in half lengthwise, and then into an even number of sections the other way. For instance, the shape above would make a sixteen page booklet.