Here's how I did it.
1. You can use Gorilla Glue or E 6000. Put the glue all over the front and back cover of the book. Split the book in the middle page to lay heavy books on it while drying. It took about 1-2 hours for books to adhere/dry to the canvases.
2. Then I used 2 different type of folds. 2 books had a simple bend over fold. Then the other two had a bend over fold followed by triangle (and alternated until all of the pages were folded). I took Elmer's glue and put it on the ends of each book at the binding (top and bottom) to help adhere the pages. In others I saw that they glued each page in but I have made several altered books and they pretty much hold themselves together if you do them correctly.
This was a pretty easy and quick wall art project. And it was inexpensive. The woman on Esty was selling them for $95 for a set of 4. Total time 1.5 hours dry glue dry time and 20min. to fold all 4 books.