The Cuban Missle Crisis and the Berlin Crisis that the other educator describes are certainly the most well-known examples of diplomatic situations of the Kennedy presidency. There were many others too that are worth mentioning. The Kennedy administration saw diplomatic efforts in Southeast Asia, Europe, Africa, the Middle East, and Latin America. Remember, this was during the height of the Cold War, a time when diplomacy likely averted a third world war.
In 1961, Kennedy met with Soviet premier Nikita Khrushchev in Vienna. They discussed ways to prevent the Cold War from escalating. Their talks helped define the independent existence of West Berlin and likely cooled many other Cold War tensions.
With Israel, Kennedy affirmed strong ties with the young nation. This was no small task to achieve in the face of a united Arab effort to undermine Israel existence. Kennedy put an end to the arms embargo against Israel and established security guarantees that endure to this day.
In Vietnam, Kennedy extended American support of South Vietnam in order to help avert a communist takeover. Vice Presiden Lyndon Johnson met with South Vietnamese President Ngo Din Diem in May of 1961. They agreed that the United States would provide technical and material support to South Vietnam to aid in this endeavor.
In response to the chaos that consumed the Congo after the Belgian withdrawal in 1960, Kennedy was very concerned about restoring order there. In 1962, he signed an order to help fund UN peacekeeping missions throughout the Congo.
Kennedy visited Mexico in 1962. There he met with Mexican president Adolpho Lopez Mateos. They discussed at length how to settle the Chamizal issue, in which Mexico claimed a small tract of land along the Texas border. Their talks led to the Chamizal Convention which eventually returned the land to Mexico thus greatly improving relations between the two nations.