How to create a Drupal book
If you have a group of related pages you can assemble them into a book.
Either choose or create a main or introductory page for your book. Edit this page and down in the Book outline section and choose create new book then this will be the parent page of all other book pages.
To add pages to this book, in the Book outline section choose the book you created in the part and these pages will be part of your book.