How did the Soviets fight the German invasion

Operation Barbarossa (German: Unternehmen Barbarossa) was the code name for the Axis invasion of the Soviet Union, which started on Sunday, 22 June 1941, during World War II. The operation put into action Nazi Germany's ideological goal of conquering the western Soviet Union so as to repopulate it with Germans. The German Generalplan Ost aimed to use some of the conquered as slave labour for the Axis war effort, to acquire the oil reserves of the Caucasus and the agricultural resources of Soviet territories, and eventually to annihilate the Slavic peoples and create Lebensraum for Germany.