Hi luannecrawford
What you need to do is go to this page
https://www.facebook.com/developers/
Login with your facebook account, than click in + Create New App
Once its created you Scroll Down to the part of the page with the title
Select how your app integrates with Facebook
Right bellow it theres the option
Website
Insert your full url ( with https:// , etc)
Save it
Now you will see the APP ID and SECRET in the top of your page, just add it ot the plugin admin config and everything should work just fine.
Let me know if any help is needed.