Short answers, pulled from the story.
The East German government built the Wall primarily to stop its citizens from leaving. By 1961, 3.5 million East Germans - about 20 percent of the population - had already emigrated to the West. The outflow was disproportionately made up of educated professionals, creating a severe brain drain that threatened East Germany's economic and political stability.
Construction began on the 13th of August 1961. The Wall stood until the 9th of November 1989, when border crossings were opened after a miscommunicated government announcement. Formal demolition began on the 13th of June 1990 and concluded in 1994.
The exact number is disputed. A research group at the Centre for Contemporary History in Potsdam confirmed at least 140 deaths. The director of the Checkpoint Charlie Museum estimated the toll at well above 200. Prior official figures listed 98 killed. The last person shot and killed at the Wall was Chris Gueffroy on the 6th of February 1989.
Over the 28 years the Wall stood, more than 100,000 people attempted to escape and over 5,000 succeeded. Methods included tunnels, modified cars, hot air balloons, ultralights, and aerial wires. At least 70 tunnels were dug; only 19 were successful, allowing roughly 400 people through.
The death strip was a cleared no-man's land between the outer and inner walls, created in June 1962 when a second parallel fence was built farther inside East German territory. Buildings in between were demolished and residents relocated. The strip was covered with raked sand or gravel to reveal footprints, and was reinforced with anti-vehicle trenches, signal fencing, dog runs, watchtowers, and bunkers.
Schabowski was the SED Politburo spokesman who, at a press conference on the evening of the 9th of November 1989, mistakenly announced that new travel regulations allowing East Germans to cross the border would take effect immediately. He had not been fully briefed and was unaware the rules were meant to take effect the following day. His announcement aired on West German television, which broadcast to nearly all of East Germany, and crowds immediately gathered at the checkpoints.