Some apps depend upon background data (transferring data when not directly in use). Restricting background data may cause those apps to stop functioning unless a Wi-Fi connection is available.
From a Home screen, swipe up from the center of the display to access the apps screen.
Navigate: Settings > Network & Internet > Data usage.
From the Mobile section, tap Mobile data usage. To see Wi-Fi data usage, tap Wi-Fi data usage in the Wi-Fi section.
Select an app (below the usage graph).
Tap Background data to turn off .
Click here for info on setting data limits and warnings, changing the usage cycle on your device and viewing data usage by app.