My favorite, across many operating systems is Xchat you can get that
Or many prefer mIRC which is
Chatzilla is also popular and I have read below this posting about its ease of usehttps://addons.mozilla.org/en-US/firefox/addon/chatzilla/
More help using chatzilla is herehttp://chatzilla.hacksrus.com/intro
The advantage of Xchat that most people will appreciate is that it has no nag ware, and never times out.
When your download of either it done, run the file, and say ok to any warning messages about file security your operating system or browser may give you. Most people can continue the installation accepting all default settings. If you do not know if you are one of the "most people" you very likely are. This is because you probably have a very standard operating system installation.
When the installation of one of these applications is done, you can come back here and click on the IRC URL once again. This could (should) bring up a one time window asking you if it should use xchat/mirc to open the link. Choose the program you just installed, and if its Xchat it should then bring you right in to the room you clicked on. mIRC has one more step I believe but I do not remember what it is.
If you are still having problems, please feel free to ask, and check back often, as answers can come fairly quick here.
If another moderator that knows what the are doing with this could edit, add, refine or correct this process for mIRC or anything else I tried to explain, please do.
Later we can copy it to the FAQ/newbie page.