Drop shadow effect
Add a drop shadow under the objects visible on the layer.

Adjusting the effect
- Distance and Rotation set how far the shadow is offset from the object and in which direction (the angle, in degrees).
- Blur softens the edges of the shadow, and Quality controls how smooth that blur looks (higher values are smoother but slightly more costly).
- Alpha sets how opaque the shadow is, from fully transparent to fully solid.
Reference
All effects are listed in the effects reference page.