This new guidance (november 2016) describes when and how to register a substance under REACH.
For the REACH legislation and its application, you can always contact the Belgian helpdesk REACH of the FPS Economy (Dutch / French). If you have complex questions about your obligations under REACH, secondarily you can also consult the helpdesk of the European Chemicals Agency (ECHA).
More guidance about the various procedures under REACH can be found on the ECHA website. You will also find there a section on the new deadline of May 31, 2018 for substances manufactured or imported in quantities of 1 to 100 tonnes per year.