right-mouse button, if the mouse has one, but most of the time either clicking and holding or control-click will bring the menu up.

In Mac OS X Leopard, docklings were replaced by Stacks. Stacks "stack" files into a small organized folder on the Dock, and they can be opened by left-clicking.Stacks could be shown in three ways: a "fan", a "grid", or a "list", which is similar to docklings. In grid view, the folders in that stack can be opened directly