Shapes are contained within stencils. And stencils are contained within the Shapes window.
Before we talk about how to get shapes, we need to make sure you understand three terms:
Shapes window: This window contains stencils.
Stencils: Stencils aren't shapes. That's important. Stencils contain shapes.
Shapes: Shapes, in Visio, are everything. But shapes aren't stencils. Stencils contain shapes.
The illustration shows the Organization Chart Shapes stencil and its shapes. Notice the two other stencils: Borders and Titles and Backgrounds. To see the shapes in either of those stencils, you'd just click on the name of the stencil.