A bit more information about exactly what you are trying to do would be helpful, as there are a number of approaches that will vary with the desired result and your level of skill/willingness to dig into the tools.
For example, a form I was dealing with recently is a saddle surface model for use by a calculus class:
The tool was Inventor, but Fusion360 would be just as good. The machining specification was the interesting part. I used the 3d adaptive with a square nose bit to rough (leaving about 0.25mm) and finished using a 1/8 round nose. The larger the round nose, the better the finish, as long as it isn’t larger than the radius you need.
If you are not sure what tool to use to build the model, or are using a particular ool, then that information will help give a more specific solution