Short answers, pulled from the story.
The invasion of Poland began on the 1st of September 1939, when German forces crossed the border and the battleship Schleswig-Holstein opened fire on Westerplatte at 04:45. The campaign ended on the 6th of October 1939, when the last operational Polish unit surrendered after the Battle of Kock, making the total duration thirty-five days.
Poland was invaded by three countries: Nazi Germany, the Slovak Republic, and the Soviet Union. Germany and Slovak forces attacked from the north, south, and west on the 1st of September 1939; the Soviet Union invaded from the east on the 17th of September 1939, acting on the secret protocol of the Molotov-Ribbentrop Pact signed on the 24th of August 1939.
Poland never formally surrendered. The last operational Polish unit, General Franciszek Kleeberg's Samodzielna Grupa Operacyjna Polesie, surrendered after the four-day Battle of Kock on the 6th of October 1939, but the Polish government refused to capitulate and instead ordered its forces to evacuate and reorganize in France.
No. This is a myth originating from a misreported incident at the Battle of Tuchola Forest on the 1st of September 1939, where the 18th Pomeranian Uhlan Regiment successfully attacked German infantry before being struck by armoured reconnaissance vehicles. Italian journalist Indro Montanelli published an inaccurate account in the Corriere della Sera, and historian Steven Zaloga identified it in his 2004 book as a story created by German wartime propaganda.
The Molotov-Ribbentrop Pact was a non-aggression agreement signed between Germany and the Soviet Union on the 24th of August 1939. A secret protocol divided Eastern Europe into two spheres of influence, assigning the western third of Poland to Germany and the eastern two-thirds to the Soviet Union. This agreement allowed Germany to invade Poland without fear of Soviet opposition and led directly to the Soviet invasion of eastern Poland on the 17th of September 1939.
Germany annexed the western parts of Poland on the 8th of October 1939, while the south-central regions were administered as the General Government under Hans Frank. The Soviet Union incorporated its occupied territories into the Byelorussian and Ukrainian Soviet republics. The German occupation ultimately resulted in between 5.47 million and 5.67 million Polish deaths, roughly one-sixth of the country's total population.