The notification, which you'll get via email and the Facebook app, shows you what kind of details Facebook shared with the third-party application or website. If sharing your email address and photo with a random app you logged into doesn't sit well with you, you can click on the Edit Settings button in the email to remove the app's permission to access your details.

You'll get a notification the first time you use your login with an app and when you reuse it after that app's access to your information has expired. Take note that you can also see which apps currently have access to your log in (and revoke their access if you want to) by going through the social network's privacy checkup.