When you register for a new account, make sure to use your real email address.  You will need to check your email to confirm it.  Otherwise, your account will expire after a few weeks.

To private chat, click on the member's name and in the profile screen click "IM".  It might or might not connect automatically.  This depends on both users browsers.  If it does not connect automatically, the other user has to click on your name and click "IM" in order to connect.