Permission settings in apps effectively limit what and how certain apps can do. For example, do you want Facebook to have access to your contacts?
If you don't want this, go to Start > Settings > Privacy and turn it off or adjust any permissions you don't like. You can adjust various easy-to-understand options on an app-by-app basis by selecting from the list of categories down the left-hand pane.
For example, going to the Location tab allows you to select which apps are allowed to use information about your location (assuming you have this enabled in the first place), and going to the Camera tab allows you to select which apps are allowed to use your PC's webcam.