Use cut tool to add extra geometry to the SubD surface

1. Select the surface and open tool menu using drawing hand
2. Grab the Cut tool and use trigger on your drawing hand to add extra geometry point to the surface geometry 
3. To complete the command, hover over to where you want the second point of the extra geometry and press the trigger on your drawing hand again. 
4. The extra geometry has been added to the surface geometry

Tip: Use this tool to make cutlines in products/cars