You can set it so that phone calls or Face Time calls or alerts will be silenced (phone and face time calls on iPhone, and only face time calls on iPad). You can set it so phone calls or Face Time calls from your “Favorites” are exempt from “Do Not Disturb”. You can also turn on “Repeated Calls” to allow an important phone calls and Face Time calls to come through if someone tries to call you repeatedly. When you have “Do Not Disturb” turned ON, a sliver of a moon will appear next to the time at the top of your screen. This process shown on iPhone 6 with iOS 8.