Coons defines a surface between four bounding curves. Coons surfaces are useful for filling in the area bounded by curves. For planar curves, Cap surface is probably a better option, although the curves must be joined into a loop first. For a grid of curves, Coons surfaces do not produce smooth results because each surface is not influenced by its neighbors. Joining curves into cross-sections and using Lofted surfaces produces better results in that situation.
When using the three curve Coons option, the ordering of the curves makes a difference in the appearance of the surface. Try different sequences until the result is correct.
Chained curves behave differently in a Coons surface than spline curves. If your surface does not look correct in the Preview, select Reparameterize curves and try the Preview again. Reparameterize curves analyzes the curves and may adjust the control points of the curves to yield a better surface result. This option affects both chained and spline curves, but the effect is stronger on chained curves.
Coons surfaces are not as common in practice as they are in mathematical discussion. Coons surfaces are approximate.