Short answers, pulled from the story.
General Michał Karaszewicz-Tokarzewski founded the Service for Poland's Victory organization on the 27th of September 1939 in Warsaw. This founding occurred just one day before the Polish capital surrendered to invading German forces.
Armia Krajowa or Home Army numbered over 400,000 members at its height making it one of Europe's largest resistance movements. Estimates suggest that actions by this group destroyed or significantly delayed one-eighth of all rail and road transports to the Eastern Front.
The Soviet Union created an alternative puppet government called the Polish Committee of National Liberation in 1944 which ensured formation of the post-war government under communist control. Soviets surrounded disarmed and arrested Underground military authority members along with civilian representatives while instituting their own administrative structures replacing existing ones.
The Government Delegate's Office restructured after leadership arrests disbanded on the 1st of July 1945 following creation of Provisional Government of National Unity in Moscow. Prominent leaders including Jan Stanisław Jankowski and General Leopold Okulicki were arrested upon revealing themselves for negotiations with communist authorities.
The Sejm declared day the 27th of September anniversary founding Service for Poland Victory organization Day Polish Underground State on the 11th of September 1998. This declaration established a national holiday commemorating the resistance movement founded on the 27th of September 1939.