Short answers, pulled from the story.
Comecon was founded at a Moscow conference from the 5th to the 8th of January 1949, with its formation publicly announced on the 25th of January 1949. The six founding members were the Soviet Union, Bulgaria, Czechoslovakia, Hungary, Poland, and Romania. Albania joined a month later and East Germany in 1950.
Stalin ordered Czechoslovakia, Hungary, and Poland to withdraw from the Paris Conference on the European Recovery Programme in July 1947 because Marshall Plan requirements for convertible currency and market economies would have drawn those countries closer to Western markets than to the Soviet Union. Comecon was established partly as an alternative framework for Eastern Bloc economic cooperation.
The Sofia Principle was adopted at the August 1949 Comecon council session held in Bulgaria. It made each member country's technologies available to the others for a nominal charge that barely covered documentation costs. The principle weakened after 1968 because it was found to discourage new research.
The EEC was a supranational body that could adopt and enforce decisions, with economic activity driven by market forces and private initiative. Comecon, by contrast, had no supranational authority and could act only through unanimous agreement among interested parties. Historian J.F. Brown described Comecon as an "international protection system" focused on bilateral aid to fulfill central planning goals, rather than an international trade system pursuing efficiency.
Comecon formally dissolved 90 days after the final council session on the 28th of June 1991 in Budapest. Its collapse followed the Revolutions of 1989, the shift to hard currency trade among members from the 1st of January 1991, and the broader liberalization under Gorbachev that included allowing members to negotiate directly with the European Community from the 25th of June 1988.
By 1983, the Soviet Union accounted for 88 percent of Comecon's territory and 60 percent of its population. The Soviet Union also possessed 90 percent of Comecon members' land and energy resources, 70 percent of their population, and 65 percent of their national income. Comecon's Secretariat was always headed by a Soviet official from the organization's creation.