Populating a communication diagram
You can populate a communication diagram with Instances. You can add an actor to the diagram as the source of an initiating message flow.
To add an instance:
1. On the Communication Diagram tab, click the 
Instance button.
Instance button.2. Click the diagram where you want to add the item.
To add an actor:
1. On the Communication Diagram tab, click the 
Actor.
Actor.2. Click the diagram where you want to add the item.