interlibrary loans
In addition to the call number, a library record will also often specify what kind of material the resource is (whether it is a book, journal, etc.) , as well as its current status- whether it is on the shelf, on reserve or signed out (it will likely give the date that it is due back as well). Make sure you check to make sure the resource is actually available before you spend hours hunting for it! 
In the event a desperately needed resource is either checked out, or is otherwise unavailable from your library, worry not! You can request what is called an interlibrary loan, a service provided by libraries that allow patrons to borrow books and other resources from libraries where those resources are readily available.
If you need to request an interlibrary loan, make sure you leave yourself enough time to obtain, and read through the resource, as it as it can potentially take weeks for the transaction to complete. More information about interlibrary loans, including how to request one, can be found here.
