A program using Natgrid will contain a section that sets values for appropriate control parameters, after which one of the gridding procedures will be invoked. In the case of using natural neighbor linear interpolation, you may not have to set values for any control parameters before invoking the gridding procedure.
To get a feeling for the available control parameters (again without worrying about understanding exactly what all of the parameters are), examine the table of control parameters at this time.
Complete details on all procedures and control parameters are presented in other modules.
Examples are provided illustrating the functionality of Natgrid. All of the examples are in the Examples module. Source codes and example plots are presented there, as well as instructions on how to create your own executables. Browse the introductory remarks in the Examples module now.
Reading through the first two modules in the bulleted list below and examining the examples cited there should serve as a quick start guide. Then, progressing through the remaining items in the list should give you a thorough understanding of Natgrid.