Which mailing lists and newsgroups are there?
There’s the newsgroup gnu.emacs.gnus (also available as gmane.emacs.gnus.user) which deals with general Gnus questions. If you have questions about development versions of Gnus, you should better ask on the ding mailing list, see below.
If you want to stay in the big8, news.software.readers is also read by some Gnus users (but chances for qualified help are much better in the above groups). If you speak German, there’s de.comm.software.gnus.
The ding mailing list (email@example.com) deals with development of Gnus. You can read the ding list via NNTP, too under the name gmane.emacs.gnus.general from news.gmane.org.