You can create two kinds of books in your table of contents:
Book with no Links: This is a book that opens or closes when clicked. When open, its content is displayed. The content can include pages and sub-books. When closed, its content collapses.
Link to Single Topic: This is a book that opens and displays a topic when clicked. Any content contained in the book is also displayed (pages and sub-books). The book can open a topic, bookmark, Web site, pre-addressed email message, FTP site, newsgroup, or remote HTML Help topic. It is also possible to link a book to a sound or video file.