Hi Mike, there isn't really any proper tutorial for that yet. I can give you a description here though.

Basically the Network surface tool takes a sort of grid or "net" of crossing curves that you have drawn and creates a surface that goes through them.

Here is one example - here I drew 5 curves, and used Network Surface to surface it:



There isn't really much to using the command itself - you just pick all the curves in the network, run Construct / Network, and it's done. The effort for this one goes into the curves that you have to create that make up the network.

One nice thing about network surface is that you can use any number of curves in it, you can add more curves to gain more control over the surface. You can have curves crossing each other, like this:



The curves should be arranged in a sort of rectangular grid - notice how above the the curves have a kind of row and column arrangement to them, they can't just be any random assortment of curves, they have to have this kind of grid layout to them.

Let me know if you have any particular questions on it.

- Michael