You need to have a server, then a channel name to join. If you look in mirc's server list, then you find a network called QuakeNet, try connect to that, when connected type:

/join #the_name_of_the_game

If you cant find what you looking for, try the help channel on that network..

/join #help

if ($me != tired) { return } | else { echo -a Get a pot of coffee now $+($me,.) }