To find out which shelf you should be searching for a book you've found listed in the catalog, examine the Copy/Holding Information at the bottom of the record. Before you start looking on the shelf, make sure the status is "checked in" and the location is the branch you are at. If not, you may have to request the book be held for you when it returns.
If the book is in fact available, check the collection and call number to see where the book should be located. Books whose call numbers start with J or E are in the children's section. For anything else, check the Chestertown Shelf Map to find out where it's located. The shelf map is available in PDF form for printing or graphical form for viewing online.