Always on Display is a feature present on most of the modern phones having AMOLED display.

It turns the screen brightness very low and Turns the only parts required for the Always on Display in a low power consumption mode.

Steps to turn Always on Display on

1.Go to settings

2.Go to 'Home screen, lock screen and wallpaper'

3.Go to 'Always on Display'

4.Turn on the switch

5.Select the design from the highlighted area

6.Click on 'Apply'

There is also a feature to schedule the timing for Always on Display to be on.

For scheduling, 

i. Click on the Display mode

ii. And select 'Scheduled display'

There are other options too as 'Move the phone slightly to display' which enables Always on Display by responding to motion of the phone and 'Display all day' which enables Always on Display to be turned on for the whole day.

Select according to your choice and enjoy!!!

Hope the article was useful ☺️.