The groupchat menu can be accessed by typing C-c C-m in the roster buffer. You can also type the commands directly, as will be shown here.
To join a groupchat, type M-x jabber-groupchat-join. You will be prompted for the groupchat to join, and your nickname in the groupchat. This nickname doesn't need to have any correlation to your JID; in fact, groupchats are usually (but not always) configured such that only moderators can see your JID. You can change your nickname with M-x jabber-muc-nick. See Configuration, for setting default nicknames.
When trying to join a room, jabber.el first sends a service discovery
info request to the room, to find out whether it exists and what
features are enabled (in particular whether the room is
password-protected). However, this can cause problems with some buggy
MUC services (or services that respond in a way that jabber.el doesn't
expect). A workaround for that is to set
t; however, the bug should be
unearthed and fixed.
Groupchat messages will be displayed in a buffer called
-*. By default, the buffer
name is based on the JID of the chat room. If you want a shorter name,
you can add the chat room to your roster and give it a name, using the
command M-x jabber-roster-change. The groupchat buffer works much
like the chat buffer. It has its own class of alerts
(see Customizing alerts), and uses activity tracking
(see Tracking activity).
Also, to save from repeating unnesesary typing you can press Tab
key to complete nick of a groupchat member that you are talking with.
You can customize your form of personal talking in MUC
jabber-muc-completion-delimiter) and form of personal talking to
customization group. Defaults are sane, so it is unlikely that you would
want to change this, but... it is Emacs!
To change the topic of a groupchat, type M-x jabber-muc-set-topic. The current topic is shown in the header line.
To leave a groupchat, type M-x jabber-groupchat-leave.
If you are the owner of a groupchat, you can change its configuration by typing M-x jabber-groupchat-get-config. A configuration form will be rendered in new buffer.
To see which people are in a groupchat, type M-x jabber-muc-names. This gives a list of nicknames, “roles”, “affiliations”, and possibly JIDs. See MUC Administration, for the meaning of roles and affiliations.