Under REACH you can have specific obligations for each individual substance you manufacture, import or use. Your obligations depend on your role in the supply chain. ECHA has developed a handy tool that helps you to clarify more these two aspects:
For the REACH legislation and its application, you can always contact the Belgian helpdesk REACH (in Dutch or French) of the FPS Economy. If you have complex questions about your obligations under REACH, secondarily you can also consult the helpdesk of the European Chemicals Agency (ECHA).