Night Shift automatically shifts the colors of your display to the warmer end of the color spectrum after dark. Warm-colored light stimulates your brain to produce more melatonin, therefore leading to natural sleepiness. This may help you get a better night's sleep.
How to enable and customize Night Shift
Go to System Preferences
In the bottom right corner, click Night Shift...
Select a schedule (i.e., Custom or Sunrise to Sunset) or choose to have the schedule 'Off'
Toggle Turn On Until Tomorrow to keep Night Shift on until you manually turn it off
Next to Color Temperature, move the slider to how warm you want Night Shift to be
If you want to manually turn on Night Shift, make sure that after sliding the custom warmth bar that you also check "Turn On Until Tomorrow" to lock it. To turn off Night Shift, just re-check 'Turn On Until Tomorrow', or move the slider all the way to the left.