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

The position of the shadow is controlled by the Distance (how far it is offset from the object) and the Rotation (the direction of the offset, in degrees). Use the Blur to make the shadow softer or sharper, the Color of the shadow to tint it, and the Alpha to make it more or less transparent. Enabling Shadow only hides the object and keeps only its shadow, which can be used to cast a separate shadow with another instance.
Reference
All effects are listed in the effects reference page.