Call Numbers = Library address
If your friends asked you to meet them at the McDonald's™ in South Bend, you'd be out of luck if you didn't know which one. There are 8 of them in the city. Even if your friends told you to go to the McDonald's™ on Ironwood, you'd still be out of luck if you don't know where Ironwood Drive is. To find where you need to go, you need an address. It works the same way with items in a library.
Hesburgh Library has over 3 million items on 14 floors. The branch libraries hold additional resources. How can you find where you need to go? It's simple: the call number for each item is its address.
Write it down!