Reserve ahead of time though they may have cars available for walk-ins. A relatively quick check-in…read moreat their kiosk/rental counter with your passport and International Driver's Permit (and if have one, the reservation printout). Get the car key, go around the kiosk to a garage for the car and off you go.
Located at the Flughafen Berlin Tegel TXL airport and a short 5-minute walk over once passed through customs. Go outside the terminal and turn right. They share an area with other car rental companies.
Note make sure flight info is in the reservation in case of delays or whatever. Otherwise, the car reservation is freed up an hour after the expected arrival.