Books

Within a category, you'll find books. Books are like containers for documentation on a specific topic.
Clicking on a book will let you view its chapters and pages.

When clicking on a section you will see the books that are contained in that section, otherwise if you click on the "Books" button in the header bar on the top right, you will see all the books currently available to you

Chapters and Pages

Usually when clicking on a book, inside of it you will only see one or more pages inside of it that are the actual content of the document; chapters are instead a way of organizing more pages, if a document is pretty big or have a big enough difference in its argument, then chapters might be made to organize its content to be more separated

Example of a book with one chapter and two pages

Example of a book with one page