You can add a shape to a sheet in one of two ways, broadly speaking. These are using code or using the Spread Designer interface.

One way is to add it programmatically, which is described in Working with Shapes in Code in the Developer’s Guide.

Another way is to add it using the Insert menu, which is described in the Insert Menu and specifically the Shape Properties dialog, which is described in Shape Properties Dialog.

You can add any number of shapes to a sheet and overlap them and adjust their appearance. For more on customizing the shape, refer to Changing the Appearance of a Shape.