A full explanation is given on the European Commission's Europa website.

You can view decree No. 2002-482 of 8 April 2002 published in the Journal Officiel de la République Française, consolidated version, on 17 July 2004, which applies the credit system to the French higher education system.

It is a personal document that provides information on the course taken in the training institution. Diploma supplements are only available for higher education in universities. The DS was introduced following the reform of the higher education with the Bologna Process. It cannot be obtained retrospectively.
For more information, please see the description of the DS on the Europa website of the European Commission, which created it.

See the national Europass site.