Tickets: You can purchase bus tickets at the ticket dispensing machines located at the airport. You need a regular fare for Berlin ABC zones, which cost 3.80 € each. You can pay by cash or credit card and can get change if you do not have exact fare. "Ermäßigt" is a reduced fare, so make sure you do not purchase it. Make sure you stamp your ticket before getting on the train at one of the red stamping machines at the beginning and end of the train platform. You'll want to keep your ticket since it is valid on any public transportation in Berlin, Potsdam and other areas outside the city for up to 2 hours after the first time you stamp it.
Train and subway: A train, usually red, runs every 30 minutes and it's the fastest and most confortable way to travel. It is marked with a red B on airport and station displays. The train leaves at 25 and 55 minutes after the hour until 10:55 PM from platforms 3 or 4. The train station is 5 minutes walk from the airport and as soon as you get out of the airport terminal, walk on the covered sidewalk along the parking lot (signs are posted). Follow this sidewalk down a flight of stairs to the underpass leading to platforms 3 and 4. Once at these platforms take the train and get off in 3 stops at Alexanderplatz (around 20 minutes). Once there, follow the blue directions with a white U on it and take the U8 subway line heading in the direction of Wittenau. This is a short trip and you will get off two stops later at Rosenthaler Platz. Once off the subway train, you want to use the exit towards Invalidenstraße (walk in the same direction as the subway train to find it). When you get on the street, go around the park and Veteranenstraße is the first street on your right.
To reach the bus stop use the northern exit of the train station (Europaplatz).
You can purchase bus tickets at the ticket dispensing machines located in the station or you can purchase tickets on the bus. You need a regular fare for Berlin AB zones, which cost 3.00 € each. You can pay cash (on the bus) or by credit card (at the machines). You do not need exact amount since change is available. "Ermäßigt" is the reduced fare valid from 6 to 14 years old. As soon as you get on the bus make sure you stamp your ticket at the yellow stamping machines on board (not necessary if you buy your ticket directly on the bus). You'll want to keep your ticket since it is valid on any public transportation in Berlin for up to 2 hours after the first time you stamp it.
From the station take the bus 142 towards S Ostbahnhof e get off at Rosenthaler Platz. Continue by walk on Brunnenstraße, along the park, and at the traffic light take the first on the right. This is Veteranenstraße, that slightly climbs along the park as well.
Alternatively take the bus 245 to Nordbahnhof. Change then to the tram M8 towards S+U Lichtenberg/Gudrunstraße. Get off at the stop Brunnenstraße/Invalidenstraße. The road that climbs slightly along the park is Veteranenstraße.