Hi Carl,
I would probably check out the user guide because we did try and highlight the many features of the Facebook integration. You can find it here:
http://www.datasprings.comuserguide...rguide.pdf There are basically multiple options... But basically if the user already exists then it will sign them in, depending on the features it might also go and find their email and sign them into the account with the matching email. Additionally you can use features to auto create the username (if they don't exist) which will create a username based on their Facebook UserID or Email (depending on the settings) and also setup the user with the first name, last name, email address, display name, etc... If you want to go a step further you can integrate Dynamic Registration and choose 'None' for the create user type in Facebook. What this will do is send all of the details to a silent post within Dynamic Registration which can then handle the creation of the user, any completion events that need to fire, or utilize any other special features of Dynamic Registration.
Thanks!
-Chad