Can you, what I'm calling, "snapshoot" videos of activity on one's iPhone screen? You know how you can press the home and side button simultaneously to take a snapshot of the screen, well, can you "snapshoot" a video of activity on your iPhone, like, a segment of a YouTube video (sometimes, something like t=1m45s on the end of a YouTube link doesn't get pushed to that time when clicked on certain devices) or "snapshoot" a process. That is, if I wanted to demonstrate steps quickly and easily I could press some buttons simultaneously and start recording, then do some things on my iPhone, then press some buttons and then it stops, and now I have a video of that activity in my videos. Is that a thing?
With iOS 11, you can use Screen Recording built in to the OS.


Go to Settings → Control Center and add Screen Recording.
When you're ready to record, swipe from the bottom of the screen to show Control Center, then tap the Screen Recording button. 3D Touch the icon for additional options such as recording the microphone.
Continue using your device and your display will be recorded.
To stop the recording, tap the Screen Recording button once more. The video is saved to your camera roll.


If your device is jailbroken, you can use Display Recorder which performs similar functionality for older versions of iOS.