An agreement about how to name and describe the data in a NetCDF file is a NetCDF Convention. The most widely used is the CF (Climate and Forecast Metadata) Convention (see CF full definition).
There is an official NetCDF Application Programming Interface (API) with interfaces in Fortran, C and C++ available from Unidata. Unidata NetCDF API also comes with some useful command-line tools (e.g. ncdump -h file.nc gives a nice summary of file contents - see ncdump guide).
There are ways also to convert a NetCDF file to ASCII or text (e.g. netcdf4excel).
For writing NetCDF files, please check through Unidata 6 Best Practices (6.8 Packed Data Values and 6.9 Missing Data Values are of particular interest).
NetCDF version 3 format is widely used. In 2008, an enhanced version, NetCDF4, was introduced.
NOTE: The NetCDF format is not formally supported by ECMWF.