The containment theory and how it was used in Europe and Asia?

If you're talking about the US containment of Communism during the cold war it was known as the Truman Doctrine. President Truman promised to contain the spread of communism across the world, and that the US would help any country that had pressure from Communism whether it be external or internal.

The US produced the Marshal Plan to stop Communism spreading in Europe because Communism came to poor people. The Marshal Plan meant that the US would provide any country who wanted help with money, advisers, natural resources, and industrial equipment. Stalin banned the Communist Eastern European countries from taking the Marshal Plan.

In Asia the US followed the Truman Doctrine by helping, South Korea in the Korean War, and South Vietnam in the Vietnam War. In both cases, the Communist north attempted to capture the Capitalist south. Also when the Soviet Union invaded Afghanistan in 1979, President Carter (and later President Reagan) provided the Mujahadin, who were fighting the USSR, with weapons.