A Call number is like an address: it tells us where the book is located in the library. Call numbers appear. Note that the same call numbers can be written from top-to-bottom, or left-to-right. KU libraries uses Library of Congress Classification for all non-fiction Call numbers to arrange it's collection on shelves. This system uses a combination of letters and numbers to arrange materials by subjects.
The library of congress classification system is arranged as follows:
You can check the details here