Facebook button? Log In or Registration

Hi guys,

We are currently testing our site and our test user, who had never tried the site before, clicked the Facebook sign in button.

The site called the Facebook app and we could see his profile picture etc was being populated into our site however it seemed that the site then required him to carry out normal registration just the same in any case.

Im now second guessing whether registration using Facebook is possible or if it is simply a method of speeding up the site access once a user has completed the registration process.

Is there any documentation that explains the flow of this? I looked but couldn't find any.

thanks,

Paula