You can organize a set of knowledge items into a book. To create a book, click the "Organize Knowledge" link on the side bar. Then click the "Create" button under book section.
On the "Create Book" page, you can select a list of knowledge items. You can also drag-drop or indent the items into a tree structure.
Click the "Create" button to create the book. You will be on the "Edit" book page.
Now the book is in DRAFT mode. After finishing editing the book, click the "Publish" button to publish the book on live site. The book is then accessible on the navigation bar of the live site.