How do I turn on night light (night mode)? Why is it helpful?

With the screen on, access the "Quick Settings" menu by swiping  the screen from top to bottom. Swipe down once more to display more icons from the Quick Settings menu.

Tap on the Night Light icon (looks like a crescent moon). Once enabled, you will notice the color of the screen change. This is helpful at night time as the phone will block specific colors that may affect your sleep.