I'll assume that you have already successfully installed jabber.el; if
not, consult the README file. Also, make sure you have
(require 'jabber) in your .emacs.
Now, type M-x jabber-customize. This brings up a customize
buffer for jabber.el. The most important variables to customize are
jabber-username and jabber-server. If for some reason
the JID of your server is not the same as its network name, change
jabber-network-server also. Save your changes, and type
M-x jabber-connect to connect.
If you do not yet have a Jabber account, you can register one. Enter
your desired username for jabber-username and the server you
wish to use for jabber-server, save, and type C-u M-x
jabber-connect. If the server supports in-band registration, you
will be presented with a registration form to fill out and send.
There you will have to enter your username again. Enter the same
username in both places, otherwise jabber.el will be confused.
If you successfully connect, jabber.el will download your roster and
display it in a buffer called *-jabber-*.
By default, you will appear as “online” to your contacts. To change this to e.g. “away”, type M-x jabber-send-presence. See Presence, for more information.
To disconnect, type M-x jabber-disconnect.