Short answers, pulled from the story.
Khrushchev delivered "On the Cult of Personality and Its Consequences" on the 25th of February 1956, at the Great Hall of the Kremlin during a closed session of the 20th Congress of the Communist Party of the Soviet Union. The session began shortly after midnight and lasted approximately four hours.
The session was closed to journalists, foreign delegates, and non-party members, and the Central Committee classified the text as "not for publication". Despite those restrictions, more than 25 million people heard the speech read aloud at party and Komsomol gatherings, and The New York Times published the full text on the 5th of June 1956.
Khrushchev accused Stalin of ordering mass arrests and executions of Old Bolsheviks and 17th Congress delegates, falsifying evidence to meet predetermined enemy quotas, exaggerating his role in World War II, deporting entire nationalities, and fostering a cult of personality that violated Leninist principles of collective leadership.
The Pospelov Commission found that over one and a half million people were arrested for anti-Soviet activities in 1937 and 1938 alone, and more than 680,500 were executed. Of the 1,966 delegates to the 17th Congress, 848 were executed.
Widespread demonstrations broke out in Tbilisi, Georgia between the 4th and the 10th of March 1956, beginning on the third anniversary of Stalin's death. Official records listed fifteen killed and fifty-four injured, but those figures are considered highly suspect, with estimates of hundreds killed. The press published nothing about the events.
The speech's policy of de-Stalinization destabilized the unpopular Stalinist Hungarian government. On the 23rd of October 1956, students demonstrated in Budapest, stormed a radio station, and tore down a statue of Stalin. Soviet tanks entered Budapest on the 24th of October, and fighting continued until the Soviet victory on the 10th of November 1956, with tens of thousands of casualties on both sides.