Adding SmartShapes automatically creates layers. Layers are basically overlays, which can be individually customized and turned on or off. Each shape and connector in the diagram forms a layer whose properties can be customized.
To know the list of layers in the diagram, in the Editing section of the Home tab, click the Layers dropdown menu and click Layer Properties...
This opens the Layer Properties dialog box, which you can use to customize the different layers in the diagram.
The Layer Properties dialog box lists the different layers in the document and allows changing the individual properties of the layers.