Airports Tegel [TXL] and Schönefeld [SXF] are right at the city border. They are easily reachable by car, public transport or taxi. More information is available at the centrail airport website.
Google Transit is available in Berlin. So you can find your way in Google Maps, the closest station is "Ostbahnhof".
Moreover, you can download any of the offline public transit apps available for Berlin, e.g. Oeffi.