Find the card catalogs that list books by title. Look at the card catalog's alphabetized drawers to locate the drawer that corresponds to first letter of the title of the book you want to find. The cards are placed in alphabetical order, so search until you find the card. Make note of the call number, the group of numbers and/or letters that is off by itself in one of the corners of the card.
Find the card catalogs that list books by author. Locate the book you want by finding the drawer that corresponds to the first letter of the author's last name. In the card catalog the author's last name appears first, followed by a comma and then the first name. The author's books appear in alphabetical order also. Write down the call number once you find the book you want.
Find the card catalogs that list books by subject. Find the drawers that correspond with the first letter of the subject such as "A" for astronomy or "P" for philosophy. Look through the subject cards to find the subcategories you need. Continue your search until you find the book you want. Make certain you know the call number of the book you want before closing the drawer.
Use the call number to find the actual book on the library shelf. At the front of each library stack or bookcase is a placard indicating the call number for the books in that section. Though they are basically in numerical order, there may be a letter in the call number that signifies a particular section, such as "J" for Juvenile.