Enter your user name and password on the Oberin start up screen and press connect. If the server is up then you will be connected. Your character will appear in the same location you were in the last time you logged off.
Choose "Log Off" or "Quit" from the file menu to disconnect from Oberin. Your character will remain in the world for an additional one minute if you have been targetted by a monster. This means that you can't log off to escape from a bad situation.
You will be automatically logged off after 10 minutes of inactivity.