Please explain the policy of Appeasement.

Appeasement in international relations means giving in to another nation's foreign policy desire in return for a concession. It is a form of diplomacy meant to avert war by arriving at an amicable solution to a conflict between states.
Appeasement has been discredited since World War II. It is most associated with Neville Chamberlain, prime minister of Great Britain in the late 1930s. Chamberlain is notorious for having tried to appease Hitler by giving him the Czech Sudetenland, which essentially meant ceding him all of Czechoslovakia. It was a backstab to the Czechs, but Chamberlain was sure it would avert another war. The "deal" was that Hitler would stop his aggressions if he got Czechoslovakia.
Chamberlain and many in the British upper classes were not opposed to a strong Germany as a bulwark against the Soviet Union.
Chamberlain was wrong that the Nazis would stop once they attained Czechoslovakia. Hitler was unappeasable and kept on going until he ignited World War II.
It is important to assess the personalities a nation is dealing with in foreign policy and not to allow wishful thinking to overcome reason.

Appeasement is a policy of giving in to demands now in return for a future promise. This policy can best be seen in the events leading to the start of World War II dealing with Adolf Hitler’s desire to control the Sudetenland, which was a part of Czechoslovakia. Hitler had been annexing land in Europe. He had moved his troops into the Rhineland, which was supposed to be demilitarized, and he had taken over Austria. He then wanted to take over the Sudetenland in Czechoslovakia because many Germans lived there. The leaders of Great Britain and France, Neville Chamberlain and Edouard Daladier, met with Hitler and Benito Mussolini to discuss this demand. An agreement was reached in 1938 known as the Munich Pact. In this agreement, the Allies allowed Hitler to take the Sudetenland in return for Hitler's promise to take no more land in the future. The leaders of Great Britain and France were hoping to avoid war by giving in to Hitler’s demands. This policy failed when Hitler took the rest of Czechoslovakia in 1939.
https://www.history.com/this-day-in-history/munich-pact-signed

https://www.thoughtco.com/world-war-ii-munich-agreement-2361475