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.1 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 or C-u C-x C-j C-c. If the server supports
in-band registration, you will be presented with a registration form to
fill out and send. There the username you chose will be prefilled.
Don't change it, 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 or C-x C-j C-p. See Presence, for more information.
To disconnect, type M-x jabber-disconnect or C-x C-j C-d.