Once you have installed and activated WordPress Facebook Login Pro you can navigate to Settings -> Facebook Login to enter your license key. The license key could be obtained in your account page.
Now in order to make the plugin functional you need to create a Facebook App
To get AppId you need to create a new app and make it live, just go to https://developers.facebook.com/and click on create new app. Choose “website app” and enter all the app details. Now copy the given AppID and Secret Key to the plugin settings page and follow the rest of instructions to make it live.
To make the app live you need to enter a valid contact email. To do that click on My Apps and open the newly created app. Then go to Settings and enter a contact email. Also enter in App Domains you website domain (Eg: timersys.com)
Lastly click on Add Platform, choose website option and enter your site url.
Now go to Status & review and make the app live by clicking the switch button:
Now you are ready to move on.