Puting FB id in a mysql player row

Hi, i'm doing a quizz (android, ios) who's almost finished.
I'm stuck since 3 days on facebook connexion.

All my question, game list, player informations are in a mysql database.
Player ID is the device unique identifier, it avoid a login screen. Players are auto connected when they're lauching the app, on your first login you just have to put your screenname.

You can have friends list in my quizz via players screenname. I'd like to have access to the player facebook ID (and put it on the dtb) and his/her friends ID to look on the dtb and look for some friendship.

I don't know if that's the better way to look for some friendship and if that's possible to do it. I did all my project in javascript and i can't found anything on facebook sdk. I also don't understand how it works with facebook. I obsiously can do a C# files just for this part of my project.

Thanks
Leo