IRC stands for Internet Relay Chat, a line-by-line typewritten communication program. It one of the oldest person-to-person real-time communications mechanisms on the internet. It is non-commercial, it is run by cooperating volunteers. It uses message "relays", that forward messages on to other relays and users as needed. EFNet is the largest affiliation group of interconnected "relays"; there are others like DALnet and UnderNet.
IRC allows you to chat person-to-group(channel), person-to-person through the public relays, and direct person-to-person privately. You can exchange files with other folks, but it's not set up to be like Napster or Gnutella, it's really designed for chatting with others.
If you already have an IRC client, connect to an EFNet server and go to
the channel #lymesters
It will ask you for a password, which is burrascano
IRC is a public chat system on the internet, supported by anonymous volunteers. IRC Client software is available for free, but there also are shareware and commercial packages.
A note about chat systems: Remember, you have no clue what the person on the other end of the wire truly is; always judge what you hear carefully. Just because someone says they're a doctor doesn't mean they really are.
Look here for IRC client software:
http://www.tucows.com/
http://www.tucows.com/circ95.html For Windows
http://macpros.mac.tucows.com/index.html For Macintosh, do a search for IRC
IRC is not ICQ nor is it AIM. Both of the latter systems are commercial, requiring you use a proprietary client which is incompatible with IRC. ICQ and AIM are funded by their advertizing value.
AOL users may have particular problems finding an open IRC server, as AOL is the origin of much misbehavior.