You can add depth to your design by adding shadows to objects.
Use the Pointer Tool to select an object.
On the Attributes
toolbar, click the Shadow tool.
Click and drag away from the object.

To adjust shadow properties,
drag the control nodes.

- or -
Use the controls on the context
toolbar.
To customize a shadow, adjust the Drop Shadow settings on the Effects tab.
To remove a shadow, select the object, click the Shadow Tool and then, on the context toolbar, click Remove Shadow.