The document discusses the call number system used in libraries to locate books on shelves. It explains that there are six main sections - fiction, easy fiction, nonfiction, reference, Spanish, and biography. Call numbers provide the "address" of where a book is located by giving its section and more specific identifying information. Fiction books are arranged alphabetically by author's last name, easy fiction uses the first three letters of the author's last name, and nonfiction uses a topic number and author name. Biographies all start with "92" followed by the first three letters of the person's last name and are arranged alphabetically.