At this conference, the Big Three had to decide what to do about Germany once it had been conquered. None of the Big Three wanted Germany to be strong again. So what they decided to do was to split Germany into four zones of occupation.
Each of these zones was going to be occupied and administered by one of the four (the French got in on this too) victorious Allied powers. In addition to dividing Germany as a whole, the city of Berlin was also to be divided. It was also divided into four zones even though it was completely within the Russian zone of occupation.