Select the Polygon tool and create a RECTANGULAR shaped object with four selection points (please note other objects when created have 8 selection points).
Now select the Arrow Tool. With this tool, when you bring the cursor near to the boundary of the SELECTED polygon, the cursor
changes shape to a cross with a DOT. This cursor signifies that you can ADD a selection point to the ploygon.
Click with this Cross with a Dot Cursor where ever you wish to introduce an additional point. Each of selection point can be selected and tweaked to CHANGE the overall shape of the polygon.