so (and this may have changed, i used to go on irc mainly in the fuckin 90s) but you need a client, back in the day the big ones were mIRC and pIRCh. i am an mIRC loyalist myself.

it comes with a server list, you just double click on a server and itll connect you. then if you type /list it will list all the channels (rooms). you can see how many people are in each channel, and you can double click on the channel list to join one. then type away