That video want help you understand anything, and the drawing is actually wrong in a couple of areas, so the guy that made it doesnt understand them either.
Pretty stock fare for Utube!
Indeed. I was going to mention that but frankly couldn't be arsed.
But since im here now, as a basic schematic of CV type carb, its absolutely fine to give you an inkling of whats going on should you be a non mechanical sort of chap, or lady.