Just go to their official YouTube profile. Some german required for the practice sessions.
The series started in 2007 and is based in Germany, but races all around Europe. The ADAC GT Masters is a "PRO-AM" Championship in which a professional driver shares a car with an amateur driver.
Each event consists of two races, with a duration of 60 minutes plus one lap. Each car must make a pit stop during each race and switch drivers. In the first race usually the amateur driver starts, if so the professional driver must drive the start in the second race of each round.