The main Gnus goal is to provide the user with an efficient and extensible interface towards dealing with large numbers of messages, no matter the form they may have or wherever they may come from.
Gnus is a fully MIME-compliant and supports reading and composing messages using any charset that GNU Emacs supports.
Extensive documentation and other resources can be found on the Gnus web site. Mailing lists and newsgroups dedicated to Gnus are referenced there.