Why the screen goes dark

When your device is idle, the screen dims and then turns off. This is normal. You can set this interval to as long as 10 minutes (learn how).

Tap the screen to brighten it after it dims. After it turns off, press the power button.

The screen also goes dark while you're on a call and hold the device to your ear, so that you don't tap something by accident. It turns back on when you move the device away.