I cannot figure out how to draw an open ended spline connecting three or more points.  I have tried reading the documentation but I find it a bit opaque.  I can draw the spline to the last point, but I can't figure out how to make it stop adding points and keep the line I have drawn.  I managed to do it once or twice, but I don't know what I did that made it work.  Where is the full explanation for how to draw an open ended spline?