If you haven't used IRC before, it may be easiest to use a web client as you don't have to install any software on your computer. Just click http://webchat.freenode.net/?channels=wikimedia-ped to join in, and then choose a username when prompted. You may be prompted to click through a security warning, it's fine.
For more information about IRC software you can install on your computer, go to the Wikipedia entry on IRC or the Meta page on Wikimedia IRC. If using dedicated software, connect to the channel #wikimedia-pedconnect on the freenode network.
More questions? Email evalwikimediaorg