Short answers, pulled from the story.
The Potsdam Conference opened on the 17th of July 1945 at Cecilienhof in Potsdam, near Berlin. Harry S. Truman had just assumed the presidency after Franklin D. Roosevelt died on the 12th of April 1945.
Clement Attlee defeated Churchill and replaced him as Britain's representative on the 28th of July 1945 following a general election held in the United Kingdom on the 5th of July 1945. Ernest Bevin took over as Secretary of State for Foreign Affairs to replace Anthony Eden.
Harry S. Truman received secret information about the Trinity test on the 16th of July 1945 which proved successful one day before the conference officially opened. Truman hinted to Joseph Stalin that the U.S. was about to use a new kind of weapon against Japan marking the first time the Soviets had been officially given information about the atomic bomb.
Germany's eastern border shifted westwards to the Oder-Neisse line reducing Germany in size by approximately 25% from its 1937 borders. Territories east of the new border included East Prussia, almost all of Silesia, West Prussia, and two thirds of Pomerania while Upper Silesia remained as the second-largest center of German heavy industry.
The Soviet Union converted several countries into communist satellite states within the Eastern Bloc including Poland, Bulgaria, Hungary, Romania, and Albania. Many of those nations had seen failed Socialist revolutions prior to World War II and refugees fled from countries occupied by the Red Army.