I need a cataloging librarian for help with Cutter numbers?

I have my cataloging exam on Tuesday, I'm studying, and I can't figure out when you are/are not supposed to use Cutter numbers. For example, in a book with an author about gl from the Czech Republic in the 1900s, which of these do you cutter (author, gl, Czech Republic or 1900s)? And sometimes I don't see any Cutter numbers at all in clification numbers - why is that? Oh please oh please let a librarian see this!!!!!