How can i open a netcdf in matlab? From url or a downloaded file?

I need to read huge MERRA data files for global solar radiation but do not even know the structure of data in the netcdf file. I have never worked with netcdf. Matlab help does not give much info. I do not understand. I tried the open netcdf example but no result and no error (ncid = netcdf.open('example.nc','NOWRITE'); netcdf.close(ncid);).

The data source url: <ftp://goldsmr5.sci.gsfc.nasa.gov/data/s4pa/MERRA2/M2T3NVRAD.5.12.4/> .

Downloaded file name example: MERRA2_100.tavg3_3d_rad_Nv.19800301.nc4. Is this even a netcdf file?

Im using matlab 2012b

Highly appreciate any help. Thanks