The Craftbook is a small tutorial on how to do various things in Junk Jack. It can be accessed by tapping the book icon on the bottom left of the screen while playing. Every so often a piece of paper pops out of a block when it's destroyed. Each of these contain a crafting recipe for a specific item, and is added to the craftbook by tapping and holding the page. Once added, you will always have that recipe in the Craftbook.
On previous versions it needed to be crafted with 2 leather and 4 paper