1. Create the book
In Content » Books, add a book and set its name, the title readers see, and its slug. Books answer below a prefix, /books unless your site changed it, so a book with the slug user-guide lives at /books/user-guide, its units at /books/user-guide/<unit> and its pages one level below.
Choose the book's layout and fill in its areas: usually an introduction and whatever your site's book template shows on the book's own page.
2. Add units
Units are the chapters. Add them inside the book, each with a name, a slug and a position, and usually a short introduction to what the chapter covers.
Plan the chapters before writing any pages. Reordering later is easy; changing slugs later changes addresses, and every link to the old ones breaks.
3. Add pages
Pages are added inside a unit. A book page is shown through its layout, like a page, so choose the layout before you write: its areas are where the content goes.
4. Publish every level
The book, each unit and each page are published separately, and a reader reaches a page only when all three are published. An unpublished book hides everything in it, however carefully its pages were published.
Order
Positions set the reading order, and previous and next links follow it. Check the order once all the pages are in.