Click the InterLifelineConnector button 
on the diagram toolbar.
Click the source element.
Drag the link to the destination element.
Drop when the destination element is highlighted.
An InterLifelineConnector link can be drawn between lifelines or from a lifeline to an interaction occurrence.
To create an InterLifelineConnector link:
Click the InterLifelineConnector button
on the diagram toolbar.
Click the source element.
Drag the link to the destination element.
Drop when the destination element is highlighted.
Related Topics:
Creating Links
Moving Links
Editing Links