It's easy and everyone ca join. Just bring your mosue pointer to chat button, and as you hover the pointer over the chat nuton, a list of the rooms would drop down. Now click the room of your choice. And a new window will open.

And then explore the buttons there to change rooms and settings.

But before all that, you need flash player from Adobe. The link to get it installed automatically is:

http://get.adobe.com/flashplayer/?promoid=BUIGP

I hope this helps!!!