Click anywhere on the canvas to create a new support point for Bezier Curve.
Two Bezier support points will form a line from one to another. Generally, Bezier curve will start at the first point and end at the last one, but not necessarily touch any other points.
You can drag the point as well to change its position and see how that affects the Bezier curve
See (currently horrible) code here! Create issues for new suggestions, will maybe implement them eventually...
Learn more about Bezier Curves in javascript.info