What happened to Poland after the German Occupation in World War II?
It was occupied by the Soviet regime and fighting continued in isolated pockets around Poland until about mid 1947. It was largely remnants of the AK against Soviet/Soviet controlled security personnel, though I stand to be corrected as my knowledge here is hazy at best.
Apparently communism appealed to the Polish People? Why was that?
No, it didn't appeal to the Polish people. Communism was forced on Poland. Had Poland prevailed as an independant and sovereign nation post WW2, it's political make-up would not have been communist. Polish communists at the time of the Rising numbered I believe in the hundreds - the appeal was therefore limited.
Who were the AK?
The AK was the Polish Home Army, arguably the largest, most effectual, coherent and homogenous underground resistance movement during WW2. With hindsight, they fought in vain. To some, they were right-wing recalcitrants and trouble makers. To those that matter or have an ancestor who fought in their ranks, the archetypal AK soldier was a paragon of military virtue and commitment to a free Poland. The AK is now but a memory and legacy held dear to some - featured as a photo on a bedroom wall of a smiling ancestor in motley combat garb - and a reminder of betrayal, folly and the injustice of war.