[Exim] SMTP Auth. a few questions...

I have searched the archives and have been able to come up with a partial
understanding of what needs to be done. A couple points I am unsure and not
clear on. is the users login id and password (shadow) being used for this
authentication? I have seen in the mailing list archives a few different
references to what people are using in their configs, but nothing that was
quite clear, and in the 'how-to' sort of style.. I seem to be trying to
piece together about 10 different postings, and am only half understanding
what is needed, so if someone can post some more info on their setups that
would be great...