Drop shadow effect
Add a drop shadow under your object's visible on the layer.

The Distance and Rotation settings define how far the shadow is offset and in which direction, so you can make it look like the light comes from any angle. Use Blur to soften the shadow's edges, Color of the shadow to tint it, and Alpha to control how visible it is.
Enable Shadow only to hide the object and keep only its shadow — useful for casting a silhouette of an object onto the ground.
Reference
All effects are listed in the effects reference page.