Apple IIGS unable to load PRODOS

[euc@cpva.saic.com]

I am trying to load an application software disk and the apple IIGS says unable 
to load PRODOS.  I have figured out that is the operating system, but I don't
know how to fix it.  How do you load PRODOS on the application software and how
do you find the execution file on the application software if you boot the
system up on a separate system disk?  Perhaps I should read a book on this
operating system.  Do you know of any simple, cheap books on Apple II system? 
signed  - just an old IBMmer......(By the way, this is not EUC - he is too
embarassed by the stupidity of this question - I am his wife.)