After a period of inactivity, the screen turns off to conserve battery power.
You can set the idle time before the screen turns off.
Home screen, swipe up and then tap
Screen timeout, and then tap the time before the screen turns off.
After you've set up
feature will be enabled by default which allows the screen to always stay on while you're holding your phone, even if you've set the screen timeout. For details, see
Edge Sense holding gesture