Click "Draw Polygon" and click the map to add a boundary for this action.
Click a polygon on the map and grab vertices to move or reshape.
Draw the area on the map. Double-click to indicate that you have finished a drawing.
You can "cut holes" in the area. Draw the outer area (including a double-click), then hold down the Alt key and draw the excluded areas (double-click to complete a hole).
When you are done, click Finish.