How can I create a video of what is on the screen?

Swipe down to access the quick settings from any screen, and then click the “Screen recorder” icon to create your recording (In the second page or click “Edit” icon to add tiles)-> select “A single app” or “Entire screen” that you want to start recording or casting with Screen Recorder-> touch “Start”. Select “A single app” will let you only screen-record or screen-share a specific app rather than your entire screen.
For additional set up options, go to the main menu -> “Settings” ->“Advanced features”->“Screen Recorder”.
Note: Available settings and menus may vary depending on device model and software version.