Click the Performance Link button 
on the diagram toolbar.
Click the source element.
Drag the link to the destination element.
Drop when the second element is highlighted.
Use the performance link to model many to many relationships between an actor and use case.
To create a performance link:
Click the Performance Link button
on the diagram toolbar.
Click the source element.
Drag the link to the destination element.
Drop when the second element is highlighted.
Related Topics:
Creating Links
Moving Links
Editing Links