If you don't want to download any clients, config them etc. you can also use the java based webchat of gamesurge.
http://gamesurge.net/chat/
First you simply load the page. [It will try to install the java application, so you must let the site to install it] You will find yourself in the "welcome" channel.
You can change your name in the "change nick to" window. [bottom right corner in the java window]
After this you simply type in /join #dominions -> this will connect you to the dominions IRC channel.
This is a very simple and easy way to use IRC.
