This console has been out for... what, six years? How is this still an unknown thing?
It records everything. However, it can't do that indefinitely because it has to record it somewhere and that's your console hard drive. If it kept everything you'd run out of space, so it records everything and - at default settings* - erases anything over 15 minutes old.
If you tap the share button once (as it says in the link), you can save the last - at default settings* - 15 minutes. You don't have to manually start it, or stop it, it just saves the last 15 minutes of what it saw.
You can directly upload the video to your social media, or trim it down to show the relevant parts then upload it to your social media.
Please do share them if they occur.
You press the Share button, then the square button, and you can do it any time in the 15 minutes after it happens. That's not exactly a frenzied and complex sequence of button presses in a narrow timeframe.
*You can adjust it to 30 seconds, 1 minute, 3 minutes, 5 minutes, 10 minutes, 30 minutes, and 60 minutes instead if you prefer.