What is the little blue line above the timeline called?
They call that a &quot;zone&quot; which is something like a selection of the timeline. The video you've linked already shows how it can be used.
I don't know why it's already there at the beginning of the video, it seems intentional and a very short Zone-bar is always there by default. That's maybe to remind the user of this feature but in any case is a strange decision in regard of user experience.
The manual indicates such a zone can also be set via the program monitor. More in the manual.