It means, that you have to paint the walls and the ceilings, in such a way, that they have he same standard as they had, when you moved in. (but not a better standard). I addition you have to clean the appartment.
Consult a local tenants association. Maybe your rent is to high. Under certain cicumstancies you can get a refund from your landlord from the time, that you moved in.
Yours, Jakob Lindberg