Connect website to FB

I need someone to fix my facebook application to work correctly when a user opens my application. There is something wrong with my project and it is not working correctly. What I need it to do is two things Check whether the user has ever logged into my app before and if not create an account where the user picks their own user name. if they already have a user account, and are in my database, then they need to go directly to [login to view URL] page. I thought I had it working, but some people that I had test it said it's not.