Short answers, pulled from the story.
Operation RYaN aimed to discover first intent and then preempt a secret nuclear attack on the USSR. This operation became the largest, most comprehensive peacetime intelligence-gathering operation in Soviet history.
NATO began its five-day exercise on the 7th of November 1983 at SHAPE headquarters in Casteau, Belgium. The event introduced new elements including coded communication formats and enforced radio silences throughout the operation.
British Prime Minister Margaret Thatcher and West German Chancellor Helmut Kohl took part in the nuclear simulation alongside United States President Reagan and Vice President George H. W. Bush. Secretary of Defense Caspar Weinberger also planned involvement until his participation was rejected two weeks into planning.
Soviet commanders placed nuclear warheads on 4th Air Army bombers after Moscow Centre sent a flash telegram incorrectly reporting an alert on American bases. A 1989 US memorandum confirmed these actions occurred following activity reported by the CIA in the Baltic Military District and Czechoslovakia.
On the 10th of October 1983, President Reagan viewed a television film titled The Day After which depicted Lawrence, Kansas being destroyed by a nuclear attack. His diary recorded that the film left him greatly depressed and primed him for the events of Able Archer 83.