I see lots of messages with quoted material in them. I am wondering
   how to have Gnus do it for me.
   
   This is Gnus, so there are a number of ways of doing this. You can use
   the built-in commands to do this. There are the ``F'' and ``R'' keys
   from the summary buffer which automatically include the article being
   responded to. These commands are also selectable as Followup and Yank
   and Reply and Yank in the Post menu.
   
   C-c C-y grabs the previous message and prefixes each line with
   `message-indentation-spaces' spaces or `message-yank-prefix' if that
   is non-nil, unless you have set your own `message-cite-function',
   which will be called to do the job.
   
   You might also consider the Supercite package, which allows for pretty
   arbitrarily complex quoting styles. Some people love it, some people
   hate it.
   
   If you decide to use Supercite, you need to modify more than just
   `mail-citation-hook'. You need something similar to the following:
(autoload 'sc-cite-original     "supercite" "Supercite 3.1" t)
(setq message-cite-function 'sc-cite-original)