Server: irc.zhzh.org, port 6667
If you aren't familiar with irc and how it works, you can go to http://irc.callete.com. Provide it with the nickname you want to go by; don't touch the "server" option, and in "channel", put #worship. That will get you to where you need to be. Some people using Safari have reported that the web client doesn't work, though, which brings us to ...
You might want to consider downloading a client, though. There's a (fairly high, but not still not infinite) limit on the number of people that can join on the web client, and using a client tends to be a bit easier than using the web interface. Some common irc clients are mIRC for Windows or Colloquy for the Mac. You can search around and find another irc client if you don't like either of these. Once you have the program all set up, you can do the following to join the channel:
To connect to the server, type /server irc.zhzh.org
To change your nick, type /nick newnickname
To enter the channel, type /join #worship
Most people tend to select a nick of the form "name|lj_name", just so people can associate a name with the username, and vice versa, but it's not obligatory. You can choose whatever nick you feel most comfortable with, really. Note that you won't be able to change your nick while the service is going on, so make sure to pick something you like. :)
For most of the service, the channel will be "moderated", which means that the only person who can speak are the people who have "ops" in the channel -- usually just ladysisyphus and rahaeli. At various times, the channel will be un-moderated, and anyone is free to speak at those times. Typing text into the entry line will have that appear exactly as entered. Alternatively, you can type "/me action" to have it display as an "action".
Regular text appears as: <burr86> hello, world!
Actions appear as: * burr86 waves to the world!
If you know irc, you probably know a bit more than this; if you don't know irc, this is really all you need to know to participate in the service. Questions, comments, clarification are always appreciated, and I'll be more than happy to tweak this post as suggestions are made.