Click the Includes Link button 
on the diagram toolbar. The button remains highlighted.
Click the use case source element.
Drag the link to the destination use case element.
Drop when the second element is highlighted.
To create an includes link between two use case elements:
Click the Includes Link button
on the diagram toolbar. The button remains highlighted.
Click the use case source element.
Drag the link to the destination use case element.
Drop when the second element is highlighted.
NB: An includes relationship link applies only to use case elements.
Related Topics:
Creating Links
Moving Links
Editing Links