The moments worth clipping are the ones you already said well: the answer to a question, the number that surprises people, the line you practised. They are sitting in the recording you just made.
Studio finds them, frames them upright around you, and writes the opening line that gives them context.
Each Short is cut from your original footage rather than from the finished video, so it keeps the full quality and it does not inherit the long video's captions or cards. You can make a Short before you have rendered anything.
Tick sentences on the Cut step to build one by hand, or take the ones Studio suggests.
A 9:16 frame is cut around where you actually are in the shot, using the filming set you told TubeSpanner about, so you are not half out of frame. Captions are sized for a phone and sit where a thumb will not cover them.
A ten minute video usually carries three or four clips worth posting. Studio shows them as a board of upright tiles, so you can watch each one and keep the ones that work.
The Shorts come from the video you already made.