Short answers, pulled from the story.
Adam Rapacki delivered a speech to the United Nations General Assembly on the 2nd of October 1957 outlining his proposal. The plan declared that Poland would not station or produce any nuclear armaments within its territory if West Germany and East Germany agreed to do the same.
The defined zone included West Germany, East Germany, Poland, and Czechoslovakia under strict prohibitions. All four countries agreed to ban production and storage of nuclear weapons within their territories.
The Soviet Union viewed the plan as addressing two critical issues: preventing West German nuclear armament and regaining prestige following UN investigations into human rights violations. On the 21st of December 1957, the Supreme Soviet passed a seventeen-point resolution including a pact of non-aggression alongside the Rapacki Plan.
United States Ambassador Jacob D. Beam sent official rejection letters based on limitations preventing effective prevention of nuclear war by the 3rd of May 1958. American officials believed accepting the plan would leave Western Europe vulnerable to communist conventional armies perceived as greater threats than nuclear ones.
Władysław Gomułka assumed leadership of the Polish United Workers' Party in 1956 after years of political activity. He used his position to assert Poland's independence from direct Soviet control through sponsoring the denuclearization plan.