Screen recording had never previously been officially supported on iOS until iOS 11. Now Apple has made it relatively simple and straightforward to record your screen on iOS devices.
Essentially all you need to do is add the record button to Control Centre. Open up the Settings app on your device and scroll down and tap on Control Centre. Then, tap on Customise Controls and select Screen Recording from the list.
Now, if you swipe up on your screen to open up Control Centre you can see the record button at the bottom. Tap the record button and once the countdown has finished your screen will start recording. Once you’re done, tap the red bar at the top of your screen to stop recording and the video clip will be saved to your camera roll.