Short answers, pulled from the story.
The Red Army occupied the entire country of Poland in February 1945. The Soviet Union annexed Polish territories in the east permanently while Poland received German-populated lands in Pomerania and Silesia as compensation.
The communist-controlled Interior Ministry issued results for the June 1946 referendum showing all three questions passed overwhelmingly but evidence later showed large-scale fraud occurred. The official election results for the January 1947 general elections showed the Democratic Bloc won 80.1 percent of the vote while Mikołajczyk resigned to protest this implausible result and fled to the United Kingdom in April 1947.
Bierut died in March 1956 and was replaced with Edward Ochab who held the position for seven months before Gomułka took power. This marked the end of the Stalinist era after hardline Stalinists were removed from power and many Soviet officers serving in the Polish Army were dismissed.
On the 13th of December 1981 Jaruzelski proclaimed martial law and suspended Solidarity. The government disallowed Solidarity on the 8th of October 1982 and martial law was formally lifted in July 1983 though many controls remained through the mid-to-late-1980s.
From the 6th of February to the 15th of April 1989 talks of 13 working groups in 94 sessions became known as the Roundtable Talks. He appointed Tadeusz Mazowiecki as the country's first non-communist prime minister since 1948 following the June 1989 legislative election.