The Difference Tool is accessable in the Shapes Tab in the Vector Tools Panel in the Side Panel. It can be used to create a polygon with the area representing the difference of one selected polygon, box, or circle from another selected polygon, box, or circle in the Shapes Layer.
Before using the Difference Tool, there must already be the two features in the Shapes Layer on which to base the difference polygon. Features can be created using the Draw Tool, or added from other vector layers loaded onto the map.
To use the Difference Tool, follow these steps:
Make sure that Shapes is selected in the Active Layer Selector in the Control Panel.
Select the feature from which the area of the second selected feature will be subtracted in the Shapes Layer.
Select the second feature to subtract from the first feature in the Shapes Layer.
Click the Difference button in the Difference Tool:
The created difference feature is added to the Shapes Layer.