Input-method documentation - where?

[David Lee Lambert]

I have a problem that may be best handled by a different input-method:  I
want to set up Emacs so that I just have to touch the keys F9-F12 with
various Ctrl-, Shift- and Alt-combinations in order to enter the accented
characters (all in Latin-1) that I would use to type German and Spanish.
However,  input-method writing is not documented in the Emacs Lisp manual.
Can anyone describe how to do it?

Alternately,  could someone give hints on how to write a short LISP
function that binds to a key and inserts a fixed string at the point?
Working one-line code would be most useful.

-- 
DLL
http://www.cse.msu.edu/~lamber45/