Tegel is the most likely place you will be arriving at. It is the largest of Berlin's airport. But it also happens to be a small one, by international standards and in comparison to Germany's own Frankfurt airport. But that needn't bother you as it is wonderfully efficient, stress-free, and easy to negotiate.
General information: Phone 0180 50 00 186. This service number has a service fee of DM 0.24 per minute (You can also get information on Tempelhof and Schönefeld airports at this no.)
You could also try their website, but be warned that it is only in German. A better option for flight information (Flugplandaten), though also in German, is the website which is actually operated by the north German television station (NDR). There is also an information-stand within the airport which is open daily until 11:00pm
You can take a taxi to get into town from Tegel which will set you back DM30 minimum or use one of the fast and frequent bus services. The 109 or express X9 will take you to Zoologischer Garten ('Zoo' for short - the western central station). From here you can connect by bus, U-Bahn (tube) or S-Bahn (train) to anywhere in the city. Tickets cost DM4.20 and are valid for two hours for all public transport.
Bus travel can be an economical alternative to the train when looking to get to or away from Berlin. The Central Bus Station (Zentraler Omnibusbahnhof (ZOB)), from which all intercity services depart, is located in the west of city. From here you catch the U2 (direction Vinetastr) to get to the centre of town. The bus companies below have regular departures from the ZOB to all major German & European cites.
For historical reasons, Berlin doesn´t have a central station from which trains to all regional destinations depart. Instead, there are a number of main stations, each of which serves different lines. Most trains to major cities pass through Zoo and Ostbahnhof; some also stop at Alexanderplatz and Friedrichstr. Other trains (particularly those to the North & East) stop only at Lichtenberg station. Travellers can use Berlin´s public transport system free of charge if they have a valid DB train ticket.