Books are a way to relate pages with one another in a hierarchically cascading chapter/section arrangement. This structure is extremely useful for creating a series of related pages on a given topic. In a book, each page may have children (i.e. “child pages.”) Each child may itself have children. So to create a chapter or section, merely make a page (the chapter), then attach child-pages to it (pages in the chapter).
Pages, chapters and sections of the book may be easily moved around. They may be moved to other areas of the book, or to another book entirely, or made into a new book in and of itself. When a page is moved, all its children (and any of their descendants) come along for the ride.
When a book page is displayed, links to its children (if any) are automatically listed at the bottom of the page (as well as links to “previous” and “next” pages, and a link to move up one level in the book hierarchy). When a page, section or chapter is moved, those lists are updated automatically, without the need to edit the parent page(s). The “printer-friendly version” link at the bottom of a book page allows you to view multiple pages of the book at once.
Another advantage to the book structure is the book navigation block (on the upper-left of a book page), which looks something like the image here on the right. It displays the name of the book in the title, and presents links to its chapters, and the hierarchy down to your current page (plus siblings and children). Pages without any children are denoted with a bullet in front of them; pages with children (e.g. sections/chapters) are preceded by a triangle (or arrowhead).
To learn how to create and manipulate book pages, read the other pages of this section (by following the right pointing link below, or use the menu links for FAQs on the upper right). Additional information about books may also be found in the Drupal handbook on books.