Shapes panel displays some built-in shapes that you can start your scene with. Simply drag them into the scene or make a new one by dragging them into the empty workspace area. This way you can quickly test the application or add a simple shape to existing scene.
The panel is called Shapes Library and looks like this:
Owlet does not (yet) provide an option to add your own shapes to the library, but we’re going to add this in the near future.