Answer:
You couldn't make any noise during office hours, (including walking heavily an flushing the toilet) no wasting food and no speaking, listening to or reading German (except for reading classics).
The most important rule was complete quiet during the work day while the workers downstairs were in the building. Anne and Margot and Peter had to complete their lessons during the day, but they always had to be completely quiet.
They couldn't walk around because they would be seen and go to concentration camp and they couldn't use the toilet unless emergency or they would probably get caught.