The easiest way to start apop up bookis to take a piece of paper and cut 2 small equal slits. Then you fold in the piece that you just cut, giving you a 90 degree angle on the inside fold.
You can glue creatures, pictures, or figures on the pop out folds to make them stand up when you open your page.
Tip: To create interest, make some of the cuts different widths and thickness. That will allow your creatures to pop up at different perspectives.
Once you have all your pages done, you can just glue the backs together to form a book. My daughter has about 5 pages done but not the cover. This is one of those projects that keeps getting more fun as she figures out new ways to do the pages and create the story.