Find the book you want in the Catalogue (Books & More) and get its call number (see eTutorials for search tips). Also check its location: McPherson, Reference, Music and Media, Priestly Law, etc. You can see this information in the main result list or the catalogue record (shown below), which you see when you click the item's title.
A call number is a unique code given to each item in the library. It identifies the subject and location of each book, journal, video, map, etc.
McPherson Library arranges most items using the Library of Congress (LC) Classification system, which uses call numbers that start with letters and also include numbers.
You can use LC Classification to see what call numbers are used for your topic.
McPherson book, using LC: PR6057 R37 I45