Create an instance of an object is actually quite simple. The drag-and-drop action consists of a short form on details of where a new object is to be placed. At the top is the usual choices of which the action applies to; "Self, Other," and "Object:," which allows you to select a specific object that this action applies to.
The actual form consists of the name of the object, the x-coordinate that it is created, and the y-coordinate that it is created. There is a check box, called "Relative", that determines whether the positioning of this object is absolute, i.e. putting "7" as the x-coordinate will place it in the seventh pixel from the left border of the room, or relative, placing the new object seven pixels from the object that the action applies to.
This action can be used in almost any event, if not all of them.