Short answers, pulled from the story.
The Potsdam Conference was held from the 17th of July to the 2nd of August 1945 at Cecilienhof palace in Potsdam, within the Soviet occupation zone near Berlin. The location placed the meeting inside territory already under Soviet control.
The Soviet Union was represented by General Secretary Joseph Stalin, the United States by President Harry S. Truman, and the United Kingdom initially by Prime Minister Winston Churchill. Churchill was replaced during the conference by Clement Attlee, who had won the British general election announced on the 28th of July 1945.
The Potsdam Declaration was issued on the 26th of July 1945 by Truman, Churchill, and Chiang Kai-shek, Chairman of the Nationalist Government of China. It gave Japan an ultimatum to surrender unconditionally or face prompt and utter destruction, and stated that it was not intended to enslave Japan. The Soviet Union was not a signatory because it remained neutral in the Pacific war at that point.
The conference shifted Germany's eastern border westward to the Oder-Neisse line, reducing Germany's size by approximately 25% from its 1937 borders and roughly 34% from its 1913 borders. The territories east of the new line, including East Prussia, most of Silesia, West Prussia, and two-thirds of Pomerania, were placed under Polish administration.
Yes. Although Truman hinted during the conference that the United States had a new weapon, Stalin already had full knowledge of the atomic bomb's development through Soviet spy networks inside the Manhattan Project. The Trinity test had taken place on the 16th of July 1945, the day before the conference opened, and Truman was informed of its success during the meeting.
France was excluded at the insistence of the Americans, who feared Charles de Gaulle would reopen decisions already made at Yalta. Additional reasons included longstanding personal friction between Roosevelt and de Gaulle, disputes over French and American occupation zones, and anticipated conflicts over French Indochina. De Gaulle regarded the exclusion as a lasting diplomatic slight.