How do I turn on iCloud Photo Library on my iPhone or iPad?

I want to sync my photos across my devices with iCloud Photo Library, how do I enable it on iPhone or iPad?

Enabling iCloud Photo Library will let your photos automatically upload to your iCloud where they can be accessed by your Mac, iPad or any other device with access to it. To turn it on, head to Settings -> Photos and toggle it on.

How to activate iCloud Photo Library on iPhone and iPad.