Link your GTalk account to Olark. We'll be sending you some special contacts that'll allow Olark to function!
Follow the on-screen instructions to log in to your Google Account, granting Olark access when asked. This works even if you have a Google Apps for Domains account!
Log into Gmail with your usual username and password.
Set your status to available (if it isn't already)
Accept ALL buddy requests. You need all these contacts for Olark to function!
Now you should now be able to chat with visitors! (assuming you've added the Olark code to your website)