How do youtube professionals record audio for their video?
If you are referring to tutorials or commentary then yes, you would record the original performance (perhaps with computer sound), while thinking of your audience. When I record tutorials for software, I often perform the example while talking, then go back and edit it down to a reasonable length. I remove unwanted sound, then re-voice the finished edit from a script (doesn't have to be fully written, can be bullet points).

This way I can make mistakes in delivery and restart as many times as I like.

Then i lay that recording back over the edited pictures. At this point I may find that I need to make the video longer to accommodate the new voice over. So there is a little bit of give and take. It is quite hard to manage picture lock without sound.