The "Constraining Path" window shows the intersection of a green surface and a red surface.  The intersection is colored blue.  A white point is located along this curve and can be controlled using the variable u0.

The "Constrained Function Values" window shows the values of the function along the curve.  Changing u0 moves the white point along this curve to help find maximum and minimum values.  A readout gives the value of the function at u0.