The animation shows various ways you can affect the graphic while working from the Text pane.
For example, when you add a new first-level bullet in the Text pane, a new set of shapes is added in the same relative position in the graphic. (In this layout, the main shape automatically includes the secondary shape, for your second-level text.)
By deleting text or changing its indent in the Text pane, you can also delete shapes. You'll get more practice working in the Text pane in the upcoming practice session.
Of course, you can work within the graphic itself to add and remove shapes and anything else you want to do — and that may be your preference. Just be aware that you can work from the Text pane to do more than type in text.