The obligation to self-quarantine applies to travellers from designated countries who have arrived in the Netherlands. Even if you were recently tested and the test result was negative you have to self-quarantine at home/your hotel/your temporary accommodation. On day 5 you can plan (another) test, if the result is negative this means that you can end your quarantine period. If you experience covid-19 symptoms you and your possible family members stay inside at least until you do not experience any symptoms anymore. If either test result is positive the Dutch governments expects you to stay at home together with your possible family members until you feel better again (24 hours no symptoms) and/or least 5 days with a negative test result.