Excerpted from The iPad Air and iPad mini Pocket Guide, Fifth Edition by Jeff Carlson
To prevent an app from slurping all of your contacts or other sensitive information, iOS requires that you give your permission before an app is granted access to your underlying data. For example, when you first open the Find My Friends app, you’re asked if you want to allow it to access your Contacts list. You can control which apps access which data in the Privacy settings. Go to Settings > Privacy and tap a category, such as Contacts, to see which apps have requested access to its data. You can block access by switching access to Off. The Location Services category determines which apps can use the iPad’s location. You probably want to grant access to the Find My Friends app (since that’s the point of the app), but you may not want Facebook to be able to include your location when you’re posting a status update. You can toggle any app’s Location Services setting to On or Off.