This depends on the landlord of your accommodation. You can move into your room at the earliest on the day your rental contract starts. In general, moving in earlier is not possible because the room will usually still be occupied by the previous tenant. Therefore, if you arrive in Berlin earlier, you will have to stay in a hostel or hotel for the first days until your contract begins.
You will receive the complete details concerning the move-in procedure and times, as well as contact information of the on-site contact persons, in the placement email before your arrival.
You can stay in your room until your rental contract ends. Please contact your landlord for details about the move-out procedure.