We use the Library of Congress classification system, which is the system most academic libraries use. LC classification uses letters and numbers to designate where the books are shelved. So, for the first book listed in box on the left, the call number is HV8073. B426 2004 REF
First, look on the ends of the shelf ranges to find the reference section. You will see REF or R on the call number label indicating this book is a reference item. So, once you find Reference, find the HV section, then look for the 8,000s, and then find 73.
The next part of the call number is the Cutter number, and Cutters are arranged alphabetically, then in decimal order. So B426 comes before I49.
After you find PS3561 I483, look for the second Cutter number F68. You have found Four Past Midnight!
Don't judge a book by its cover isn't just a cliche, it's good advice. Anyone can write and publish a book. You still need to think about what you're reading and be critical. For example, a book about Scientology by the founder L. Ron Hubbard is going to be very different from a book written by a former adherent of Scientology, or one written by a professor of theology. All three are valid sources, but you must decide which is the best to cite for the point you are trying to make.