IRC, Internet Relay Chat, is one of the greatest communication platforms on the Internet. You normally connect to one of the IRC servers using tools like Mirc which have been designed for that purpose. Once connected, you can start by retrieving a list of open channels on that server - and connect to some that sound interesting. Once in a channel you can chat, send private messages to other users, and transfer files to users other users or channel bots.
Chatzilla opens in a new window, you should take a quick glance at the preferences before you connect to a server. If you do not want to exchange files you should disable DCC in the options. Supported Networks are Efnet, Dalnet, Quakenet and Undernet plus some lesser known ones. Clicking on a link of a network connects to one of its servers. It is now time to join channels, do so by clicking on IRC > Join channel.
The channel search looks similar to the one offered by Mirc: type in a word (xbox, games, counterstrike) and the channel list will display every channel with such a name or topic. Double-clicking a channel in that list joins that channel and you see the list of users on the right side and the main channel window with the public chat in the middle. If you right-click a user you can open a private chat or send that user a file for instance.
I like this add-on, as I sometimes search for specialized information and find that only on IRC. For example, if you need coding help you might want to join a channel like #html or #php. The people there are skilled and willed to help you if you phrase your requests properly and in a friendly tone.