As the subtenant, you are responsible towards your landlord for the apartment and furnishing. For this reason, it is important that you arrange a personal liability insurance which covers the liability for possible damages done to the rental property in Germany.
A personal liability insurance is low cost coverage for damages caused by those accidents which so easily happen in everyday life. The insurance only costs approx. € 50.- up to € 100.- per year and can be arranged with almost any German insurance company.