There a link at the top of this page, near the wiki link. Input your username. There are usually some people on the IRC, depending on what time it is. There are PPC participants all over the world, so unless some are busy there's almost always at least one person hanging around.

While IRC is slightly complex (if you want to set up your own room with special features, like dice rolling for games... I play Dungeons and Dragons over it!) just chatting in the PPC room is simple and requires pretty much no experience with IRC at all. Just click the link, it launches in your browser, enter your username, and go! :)