What decisions were reached at Yalta and Potsdam?
The conferences at Yalta and Potsdam were the two last major conferences of WWII. History books usually emphasize the Yalta Conference much more than the Potsdam Conference.
The Yalta Conference was held in February of 1945. At that point, all of the “Big Three” were still in power and all of them attended the conference. The Allies were still fighting Germany. At Yalta, they decided to divide Germany up after the war. There would be four occupation zones, with one each to be run by the USSR, the US, England, and France. They also decided that the Soviet Union would get to control Poland but that it would allow all the other countries of Eastern Europe that it occupied to hold democratic elections. Finally, the Soviets agreed that they would enter the war against Japan (the US had not yet even tested an atomic bomb) no later than three months after Germany surrendered. Yalta is now mainly remembered as the conference at which the allies split Europe up into communist and non-communist spheres of influence.
The Potsdam Conference was held at the end of July 1945, but many things had changed by then. Germany had surrendered. President Roosevelt was dead. Winston Churchill had been defeated and was no longer prime minister. The US had developed the atomic bomb. So this was a very different conference. The main two decisions from this conference were first, that the Soviets would get a great deal of German property as reparations for their war losses and second, that the allies would continue to demand that Japan surrender unconditionally.