Hi there,
Berlin's integrated public transport system (BVG) is the best way to get about within Berlin. The system has an interconnected three-zone system (ABC) which only requires one ticket, allowing you to hop from bus to underground (U-Bahn) to surface rail (S-Bahn) and tram with one ticket. Trams are fast and convenient and small ferries will get you across
Berlin's lakes.
Hope this helps
Vacationbuddy