The way that you can login to Facebook is to go to the security settings at the top right hand corner, and click settings, security and login.
Signing into Facebook is safe. It is secure and convenient to do. People can sign into to many different media accounts using the social media credentials they have. This helps you to be safe against breaches.
You can connect to Facebook API, by goin to link developers.facebook.com to create an account there. Go to link developers.facebook.com/tools/explorer, go to my apps drop down in the top right hand corner, select add a new app, then select get token.
Facebook ID is the number identification or user ID that connects you to your Facebook profile.
More Facebook Login Information:
Facebook Login Video