QA uses Mozilla's IRC server for real-time communication and collaboration. Many of the regular QA events revolve around IRC in some way - both Test Days and Bug Days happen over IRC.
In order to get started on IRC, you need an IRC client. You can use Chatzilla, Mozilla's own IRC client, or any other IRC client you choose to connect to Mozilla's server.
The #qa channel is our central meeting place on IRC, but specific channels are reserved for and used with regular events, such as #bugday and #testday.
You can learn more about using IRC at http://www.irchelp.org/, which includes an introductory guide for new users.
You can learn more about the Mozilla IRC server at http://irc.mozilla.org/
1. If you wish to use SSL, enable it in your client and choose port 6697.