iOS 11 comes with a handy new Control Center function that allows you to record what you're doing on your screen. It's great if you want to capture gameplay, walk someone through a tutorial in an app, demonstrate a bug, and more, and it's available on iPhones and iPads running iOS 11.
If you don't have the screen recording icon in Control Center, you can add it in the Settings app.
While screen recording is turned on, a red bar is plastered across the top of the display so it's clear when you're recording and when you're not.
There are a few options that are available when making a screen recording, which can be accessed directly in the Control Center. To bring up these options, simply 3D Touch on the screen recording icon.