The Marshall Plan can be seen as a Cold War tactic because the United States federal government tried to prevent the spread of communism through this law.
During the Cold War, the US government adopted a policy of containment. This idea focused around preventing the spread of communism to countries all over the world. One way that the United States planned to do this was by providing financial assistance to countries that were in jeopardy of being taken over by the communist Soviet Union.
This is exactly what the Marshall Plan accomplishes. The United States agrees to give $13 billion in economic aid to countries all over Europe (like Great Britain, France, etc.). This assistance was meant to ensure that each countries capitalist system remained in place.