I'm sure this has been asked before... but If I have a site and want a channel devoted to the site (members from the site can join it) how do I make one?

This consists of two steps:

1. Set up a channel on an IRC network of your choice.
2. Upload a Java applet to your website and let your visitors use it to reach your channel.
   
   Freeware applet: PJIRC
   Shareware applets: JWIRC, jIRC.

For more information search these forums for the word "applet" or refer to the documentation of the applet you decide you try out.

https://forums.mirc.com/showflat.php?Cat=0&Number=94434&an=0&page=0#94434