If I have created a polygon pour how do I modify the shape? I know you can move individual vertices but how do I change the shape by adding extra vertices?
Select 'Edit>Move>Polygon Vertices' (shortcut "MG"). Right Click on the polygon. Selection handles will appear on each polygon side. To add a vertex, left click (don't hold) on the middle handle on one of the sides, and then move the handle to form a new vertex - left click again to drop the vertex in the new location. Repeat as desired. Right click when you're done, and answer "yes" when it asks if you want to repour.