Short answers, pulled from the story.
The Warsaw Pact was signed on the 14th of May 1955 in Warsaw, Poland. The eight founding members were the Soviet Union, Albania, Bulgaria, Czechoslovakia, East Germany, Hungary, Poland, and Romania.
The Warsaw Pact was created directly in response to West Germany joining NATO on the 9th of May 1955. Soviet leaders feared a remilitarized Germany and had repeatedly sought diplomatic alternatives, including proposals for a neutral reunified Germany and a request to join NATO themselves, all of which Western powers rejected.
The Warsaw Pact's largest military engagement was the invasion of Czechoslovakia in August 1968. All member states participated except Romania and Albania. Albania formally withdrew from the pact less than one month after the invasion.
Romania obtained the complete withdrawal of Soviet troops from its territory in 1958 and by the early 1960s had freed itself from Soviet satellite status while remaining a formal pact member. By December 1964, all Soviet advisors had been withdrawn, Romania refused to participate in joint military exercises after 1964, and the country developed its own independent military doctrine using locally produced equipment.
On the 25th of February 1991, the pact was declared dissolved by joint declaration of the defense and foreign ministers of the six remaining member states at a meeting in Hungary. Czechoslovak President Vaclav Havel formally ended the treaty on the 1st of July 1991 in Prague, after 36 years of existence.
Seven Days to the River Rhine was a Warsaw Pact nuclear war plan that envisioned a short, swift invasion and capture of Austria, Denmark, Germany, and the Netherlands east of the Rhine. It assumed nuclear weapons would be used in response to a NATO first strike. The plan was among roughly 1,300 declassified documents published by Poland's Institute of National Remembrance in January 2006.