Get an IRC client (see the links below for specific clients) and logon to irc.freenode.net with a suitable nickname. If you've never used IRC before, don't worry, it's easy enough that even your parents can do it.
Configure your client for the freenode network and join the channel #geozone. This process will differ from one client to the next; the important part is the network and channel name.
Your client of choice may already have several different IRC networks in its default configuration, but it probably won't have very many (if any) channels configured (with the possible exception of one or two help channels in the case of chatzilla). There should be an editing facility for the network, server, nickname, etc, or you can use the command-line (all IRC commands begin with a slash), eg:
/server irc.freenode.net /join #channel_name (eg, #geozone, #code-hell, #gentoo-server, etc) /nick new_nickname
and most importantly :)
/msg chanserv help /msg nickserv help
Once you connect to freenode, you should see the banner message from the server you connected to, which you can double-check to make sure it's actually freenode. It should look something like this:
Welcome to the Internet Relay Network Your host is zelazny.freenode.net running dancer-ircd-1.0.35 via dircproxy 1.0.5 This proxy has been running since Mon, 16 Feb 2004 21:36:54 -0800 zelazny.freenode.net dancer-ircd-1.0.35
All IRC clients should support the same basic commands, as well as their own specific options. The only command you need at first is the /join command (all IRC commands begin with a slash). So once you're connected to the freenode network, issue the following command from the IRC prompt in your client:
/join #geozoneChannel names always begin with a # symbol; there are many more IRC commands (which you can read about).
See the links below for more comprehensive help docs. If you have the full Netscape/Mozilla installed (regardless of OS), then you already have an IRC client. See the Chatzilla page for more info. Otherwise, use your favorite methods of finding and downloading software, and look for one of the following: