I struggled with this one too. Here's what I did:
1) Sign in to your Facebook account (must be a personal profile, not a page)
2) Search for Developer App and enable it (allow it to view your basic info)
3) In the Developer App, click "Set Up New App" button. Create a name for your Facebook app (doesn't really matter what you call it). Click the "Create App" button.
4) Facebook may ask you to prove you're human by entering a verification code it will text to a mobile phone number associated with your account.
5) After your "app" is created, it will give you an app ID and app secret at the top of the page. Just copy and paste those into this plugin's settings page and click update.
Hope that helps!