Short answers, pulled from the story.
The definitive German Instrument of Surrender was signed at the seat of the Soviet Military Administration in Berlin-Karlshorst on the 8th of May 1945. A preliminary surrender had been signed the day before in a red brick schoolhouse in Reims, France, that served as the SHAEF headquarters.
The Soviet Union refused to recognize the first surrender signed in Reims on the 7th of May 1945, arguing that the text differed from the European Advisory Commission's agreed document and that the Soviet representative had not been empowered to sign. The Soviets insisted the formal surrender take place in Berlin, the seat of the Nazi government, to reflect the Soviet Union's central role in the victory.
Marshal Georgy Zhukov signed on behalf of the Soviet High Command, and Air Chief Marshal Sir Arthur Tedder signed as Deputy Supreme Commander of the Allied Expeditionary Force. General Carl Spaatz signed as a witness for the United States and General Jean de Lattre de Tassigny as a witness for France. Field Marshal Wilhelm Keitel, General-Admiral Hans-Georg von Friedeburg, and Colonel-General Hans-Jürgen Stumpff signed for Germany.
The surrender took effect at 23:01 CET on the 8th of May 1945. The Berlin document was back-dated to show signing at 22:43 CET on the 8th of May, though the physical signing was not completed until nearly 01:00 am on the 9th of May due to delays in resolving the Allied signatory arrangements.
When the Berlin surrender was physically signed, the time in Moscow had already passed midnight, placing the event on the 9th of May 1945 by Soviet reckoning. The Soviet government did not recognize the earlier Reims signing, so it observed the 9th of May as Victory Day. Western Allied leaders had already announced the end of the war on the 8th of May, establishing that date for VE Day in the West.
The Flensburg Government was the rump Nazi administration formed by Grand-Admiral Karl Dönitz after Hitler's death on the 30th of April 1945, established at Flensburg near the Danish border. None of the Allied governments recognized it as legitimately representing Germany. On the 23rd of May 1945, Dönitz and other former Nazi officials were arrested in Flensburg and taken into captivity as prisoners of war.