How do I add define a key for a particular mode to say, insert stuff?

Hi:

I am using XEmacs 21.4 (patch 12). How do I define a key say F12: such
that in LaTeX mode pressing that key will result in the insertion of the
preamble of a general LaTeX document into the current buffer, and if I
am in the CC mode pressing the same key will result in the GPL being
inserted. 

I am very new to emacs-lisp so I would be greatly benefited with
explicit instructions.
Thank you

Hareesh Nagarajan
-- 
http://puggy.symonds.net/~hareesh