Click the Swimlane button 
on the diagram toolbar.
Click on the diagram to create the element.
Resize the swimlane by dragging the corner of the element to the desired size. The element grows or shrinks in the direction of the cursor.
To create a swimlane, choose one of the following methods:
Using the diagram toolbar button:
Click the Swimlane button
on the diagram toolbar.
Click on the diagram to create the element.
Resize the swimlane by dragging the corner of the element to the desired size. The element grows or shrinks in the direction of the cursor.
Using the diagram context menu:
In Diagram view, right click on the background.
From the context menu, select New > Swimlane.
Using the element context menu:
In the UML Navigator view, right click on the activity diagram that will contain the new swimlane.
From the context menu, select New > Swimlane.