email signature file

Tue Feb 6 19:30:01 2001

Hi all,
Just started using the gnupg keys and had a basic question: How do I setup my
gnupg keys as the signature file ? I see everyone has, so then how is it done ?
I`m using kmail on mandrake 7.1. The error I get is- this is a directory and
not a file. 
            Thank you, Chronos.