BVG app … gives travel options/routes/timetables etc. for trains, trams and buses. Also tickets CAN be bought through this app, and are immediately valid.
The city of Berlin and the surrounding suburbs have been organized into three tariff zones A, B and C. You can buy tickets for the combined zones AB, BC or ABC, as needed. Adults pay regular fare; The reduced fare is valid for children aged 6 to 14. Children under 6 do not need tickets.
Berlin's inner city up to and including the S-Bahn (urban rail) ring
outside the S-Bahn (urban rail) ring
up to the city boundary; Airport Berlin Tegel TXL is located in this zone.
Greater Berlin area (approx. 15 km around the city of Berlin), including the City of Potsdam and Airport Berlin Schönefeld SFX
From August 1, 2019, all school students studying in Berlin, or who live in Berlin and study in Brandenburg, can apply for a free student travel card for the Berlin AB area from the city’s transport association, the Berliner Verkehrsbetriebe (BVG). To purchase it you need to provide a Student Identity card '
To purchase a Monthly Student Travel card you will need a Student ID card "Schülerausweis". You can ask it at the secretarial support team.
Monthly Travel card (adults) allows immediate family members to travel free with the cardholder at weekends and also after 8pm on weekdays.
A day ticket/Tageskarte (8.60€ for AB Ticket / 9.60 € for ABC ticket) will allow an adult to travel with up to three children (through age 14) for FREE at all times, great deal.
If you buy a ticket from a ticket machine, remember to ‘validate’ it before you travel (a smaller stand alone machine usually near the ticket machine)