There are 3 Airports in Berlin:
Tempelhof (with a subway connection to the city)
Tegel (with a bus connection to the city) and
Schoenefeld (with a train connection to the city)
Most visitors arrive at Berlin at Tegel. Take the Bus to "zoologischer Garten" and than change to the Bus No. 100
The Bus No 100 is the cheapest way to take a real good sightseeing tour (2,30 Euro). It is a regular bus but you'll see all the attractions like Siegessaeule, Schloss Bellvue, Reichstag, Brandenburger Tor and so on. Make a stopover at Potsdamer Platz or Unter den Linden . . .

