The approach to World War II by many Western historians is overly simplified: there was one aggressor - Germany and one victim - Jewish people in teh effect of Holocaust. This so-called "Allied Scheme of History" was criticized by Norman Davies and other historians, experts on Central and Eastern Europe.
If Poles are mentioned, it is either in regard to the beginning of the War, since it began with the invasion of Poland, or much worse: as collaborators with Germans against Jews, the only victims. Very rarely is there any analysis of the complexity of the war in Eastern Europe, not only in the case of Poland but also Ukraine, Baltic countries, Finland etc. The Soviet Union is usually seen only as an ally of the West, without emphasis on its earlier role as an ally of Hitler's Nazis before it was attacked by Germany in 1941. The latest history seen all through the Eastern Europe block (Soviet Satellite countries) was also falsified in a similar way as Western history. There was no mention of the Soviet invasion or it is justified as protection of minorities against the Nazis.
The case of one enemy and one victim does not really apply to Poland. Not everybody realizes that a similar situation happened when Poland was attacked by Germany on September 1 and then by the Soviet Union on September 17. These countries then divided Poland according to the secret appendix of the Molotov-Ribbentrop Pact.
The treatment of Poles depends on where you lived. The western part of Poland was annexed by Germany, whereas the central part of Poland with Warsaw and Krakow was placed under a German administration called the General Government. Whereas France, Hungary or Slovakia were allowed to keep some limited national identity, Poland was not. Hans Frank, a German lawyer, was appointed as the general governor of Polish regions. Germans did not even try to pretend that Poles had any say about their country.
The territories that were annexed to Germany were divided into separate administrative units with capitals in Poznan (Wartheland), Katowice (Regierungsbezirk Kattowitz) and Gdansk (Reichsgau Danzig-Westpreussen).
The regions that were occupied by Soviets until the Soviet Union was attacked in 1941 were also divided, with Vilnius being "given" to Lithuania, of course after Lithuania was already under Soviet control. The war in the Soviet-occupied zone deserves a separate article, so I will concentrate here only on the areas occupied by Germans.
Life was different in annexed areas compared to the region under control of General Governemnt, in some aspects it was worse, in other aspects better, but everywhere quite bad. Poles were considered the servant class, with Polish intelligentsia and spiritual leaders (priests) being slowly liquidated and not replaced since all universities and any institutions of higher education were closed.
Poles who were living under the control of the General Government were able to speak Polish on the streets and at schools (although only primary and secondary education was allowed), whereas Poles in the regions annexed by Germany were forbidden to speak Polish not only at school and work but also at home. Residents of Warsaw were the most affected. Warsaw was bombed at the beginning of the war and also at the end (Warsaw Uprising), and her citizens were much more exposed to harsh treatment - body and house searches, many were being rounded up on the streets and sent to labor camps, since Warsaw was considered a center of the Polish resistance against Nazi. In Krakow, which was the capital of the General Government, life was much more quiet; the coexistence of both Polish and German people was much more peaceful, both Polish and German were heard on the streets and in the cinemas and theaters. Poles and Germans even shared the same seats on the trams. Krakow remained largely intact during the war.
Poles in regions annexed to Germany enjoyed relative safety in some aspects no street roundups, no German bombardment but they were treated harshly if they wanted to claim their "Polishness". Poles from territories annexed to Germany lived in constant fear of being resettled: hundreds of thousands of people especially from Poznan were thrown out of their houses, carried in animal wagons to the regions under control of the General Government, and left without any means of support. The German officer who helped Szpilman (The Pianist) also witnessed scenes of expulsions of Poles and described it bitterly in his letters and memoirs.
My mother, 9 years old, remembered her first day in German school. She did not understand German at that time, and she asked her mother why the teacher was constantly screaming about the pipes (pipe in Polish is "rura"). She did not understand that he was just yelling at the students to be quiet ("die Ruhre")! She soon learned German very well, partly at school, partly by reading German novels while watching the geese. She became so good that the school principal considered sending her to a school for German teachers, until it was revealed that her family was all Polish!