For the first part of your post you might begin here:
And here for the 2nd:
They are asking HOW the Cold War changed the alliances that had formed during WW2. First you need to know who the US was allied with during WW2. Why did these ties change?
Then they are asking how the Cold War policy of the US influenced international decisions/relations. How did the relationship changes effect the rest of the world?
Here are a number of great sites on the Cold War.
Describe how the Cold War ideology that crystallized after WWII changed wartime alliances that had existed during the war.
During WWII, Germany and Japan were our enemies, while the Soviet Union was one of our allies. The Allies worked together and defeated Germany and Japan. We divided Germany into four parts, with three parts governed by France, Great Britain, and the U.S. We believed that we needed to help Germany become a self-sufficient democracy -- which soon became reality. The fourth part, East Germany, was governed by the Soviet Union. It also took over eastern European countries, and made them dependent upon the Soviets. It was obvious that they also wanted to take over other parts of the world. Thus the Cold War was begun with the two major powers -- the U.S. and the Soviet Union verbally threatening each other. Everyone was afraid that the other side might use nuclear weapons.
o Describe how American Cold War policies and practices influenced international relations from the late 1940s to the mid-1950s.
International relations were dictated by our desire to keep as many countries on our side as possible. We gave financial aid to many countries and fought the Korean War in order to keep countries out of the Soviet sphere and on our side.
For more information, check out this article.