Short answers, pulled from the story.
The Berlin Wall fell on the 9th of November 1989. Harald Jager, commander of the Bornholmer Strasse checkpoint, ordered the gates opened at approximately 22:45 that evening after crowds of East Germans overwhelmed border guards who had no authorization to use lethal force.
The fall was triggered by a miscommunication at a live press conference. Gunter Schabowski, who had not been briefed on new travel regulations, misread a note from Egon Krenz and told reporters the rules allowing East Germans to cross all border points were effective "immediately." News broadcasts carried this announcement across East Germany, causing crowds to rush the checkpoints.
Gunter Schabowski, the outgoing party leader in East Berlin and the SED's Secretary for Information, made the announcement at a press conference beginning at 18:00 on the 9th of November 1989. He had not participated in drafting the new travel regulations and had only received a summary note from Egon Krenz shortly before taking the podium.
The Pan-European Picnic was held on the 19th of August 1989 on the border between Austria and Hungary. Organized around an idea by Otto von Habsburg, it opened the Iron Curtain and set off a chain reaction in which tens of thousands of East Germans traveled to Hungary seeking passage to the West, eroding the foundations of border control across the Eastern Bloc.
Informal demolition by so-called Mauerspechte (wallpeckers) began on the evening of the 9th of November 1989. Official dismantling by East German Border Troops started on the 13th of June 1990 in Bernauer Strasse, using 175 trucks, 65 cranes, 55 excavators, and 13 bulldozers. The work produced an estimated 1.7 million tonnes of rubble, and the last section of the Berlin-Brandenburg border wall came down in November 1991. Full demolition was completed in 1994.
the 9th of November carries multiple painful historical associations in Germany. The date marks the Kristallnacht pogroms of 1938, the Beer Hall Putsch of 1923, the execution of Robert Blum in 1848, and the abdication of Kaiser Wilhelm II in 1918. Nobel Laureate Elie Wiesel noted that the date had already entered history 51 years earlier as Kristallnacht. Germany chose the 3rd of October, the date of official reunification in 1990, as German Unity Day instead.