IRC is used for real-time chat with groups and sometimes one-to-one. If you are already familiar with IRC and have a client to hand, point it to irc.freenode.net and join #openrightsgroup ... read on for more detailed instructions.
If you've never used IRC before and would just like to join the chat room to start hanging out, you can use the a web interface which does not need extra software.
If you'd like to hang out in the chat room more often, or perhaps would like to get more into other IRC communities too, then you probably want an IRC client. This is software which runs on your computer and connects you to an IRC network.
These are in alphabetical order rather than any preference.