Editing complex masks overview
Complex masks are defined by Bezier splines and B-Splines, which are built with control points. Each control point in a complex mask defines some sort of corner or curve, and the actual spline that makes up the shape connects these control points together like a connect-the-dots drawing. The control points determine the shape and curvature of the spline.
You can modify a spline by dragging its control points and adjusting the tangent handles attached to each control point. You can transform multiple control points simultaneously, and you can add, delete, and lock control points.