BVG

The Berliner Verkehrsbetriebe (yellow logo) offer metros services (U), trams and busses (numbers or combination of letters and numbers) throughout the city of Berlin. The city area is divided into zone A, B, and C. The inner S-Bahn ring is covering zone A.
The BVG offers tickets at the yellow ticket machines found at public transport stations.

Subscriptions and tickets at the BVG Website
BVG Ticket App at the Apple Store or Google Play Store.

VBB

The Verkehrsverbund Berlin-Brandenburg (red logo) offers regional trains (RE, RB) at the states Berlin and Brandenburg. The VBB offers tickets at red ticket machines found at public transport stations.

S-BAHN BERLIN

The S-Bahn Berlin (green logo) offers S-Bahn lines (S) at the state of Berlin. The ring lines S41, S42 (clockwise and counter-clockwise) run around the city center.