To create Facebook APP ID follow the instructions https://developers.facebook.com/docs/apps/register
In case you get "Can’t login with Facebook. Please, try again later." message:
1) Make sure that file_get_contents() function is enabled in the server configuration.
2) Make sure that you made your APP public
3) Make sure that you added Valid OAuth redirect URI to My account page and Checkout page if you want to use FB login button there