If you want to find out where your friends are chatting (and maybe join them) here's what you need to do:

Click the People or Community menu at the top of your screen and click Locate Member/Buddy Online (or just press the Ctrl and L keys together). Type the screen name you're looking for in the box that appears, and click OK. You'll find out whether your friend is online, and if so, whether they're in a chat room in which you can join them.

Note: You won't be able to join them if they're in a private chat room, but you can still send them an Instant Message and ask them to invite you in.

Another way to find your friends online is to add them to your Buddy List. You can set up your Buddy List when you sign on. When you see a friend appear on your Buddy List, simply click once on their screen name and click the Locate button.