They are little bookmarks that go over the corner of a page. There are different versions out there, these follow the instructions from our Stampin' Up! demo magazine and use a square of designer paper (mine is 5x5"). You fold this in half and then in half again, so you end up with a square a quarter of the size of your original one. Unfold and cut one quarter out along the fold lines. Fold the two flaps back down and adhere to make a little pocket. Then you're free to embellish, just try and keep the embellishments fairly flat, so the bookmark slides into the book easily. I also saw these bookmarks here, which ultimately inspired me to give them a go, and I had great fun making them :) They're really quick, cute and use up scraps very nicely.
Thanks for looking!