Each item in the library has its own unique call number...an address that tells you where the books is located in the library.
Call numbers can be found on the spines of books and in the online catalog - they can be written from top-to-bottom, or left-to-right!
Just follow letters then numbers. For example, if you have book from the Main Stacks with the call number BL2525 .O94 2009, then you need to go to the Main Stacks and find where the BLs start, then within the BLs find 2525, then within the 2525s look for .O94.
For more information about call numbers, view the Call Number Basics