CDO (Climate Data Operators) is a free and open-source software that provides over 600 command line operators for performing statistical analysis and data manipulation on climate and weather data. It allows users to select, subsample, interpolate, perform arithmetic operations and simple statistical analysis on netcdf and grib files. Some basic CDO commands include using conda to install CDO, using cdo info to get file information, cdo merge to combine files, and cdo copy to change file formats.