Actors
An org-unit represents the role played by something or someone within the enterprise environment of the modeled system. It is related to the business activities of the enterprise, and interacts with the system in different use cases. It can be an element in the enterprise structure such as a division, a department, or a workstation.Examples of actors:
To create an actor in a use case diagram:
1. In the object toolbar, click Actor 
2. Click in the diagram.
The Add Actor dialog box opens.
3. Enter the name of the actor, “Receptionist” in this example.
4. Click Add.
The actor then appears in the diagram.