XF 1.2 Any simple articles/documentation regarding Facebook logins?

I need something simple that explains how the Facebook login works with Xenforo. By simple, I mean I know practically nothing about FB or logging in from there to begin with. Any suggestions on where I can find it here? Or has someone posted on it in the forums? Please provide link. I did look in the manual, but did not see anything about FB logins. It may be there, but I did not see it.