The overall cause of the Cuban Missile Crisis was the Cold War conflict between the United States and the Soviet Union. There are other causes, but they all stem from this cause. The main effect of the crisis was to make the two countries more cautious about coming into conflict.
During the Cold War, the US and the USSR were in competition to dominate the world. The US was capitalistic and democratic and thought that communism was evil and aggressive. The USSR was communist and thought that A) communism would inevitably take over the world and B) the US was out to destroy it. These attitudes brought the Cuban Missile Crisis about.
Because the US feared the USSR, it placed nuclear missiles in Europe that could hit the Soviet Union. Because the Soviets feared the US, they tried to put nuclear missiles in Cuba so that they could threaten the US as well. Because the Americans feared and distrusted the Soviets, they worried that the USSR would actually use the missiles in Cuba. Because the US feared the Soviets and though they were out to take over the world, they felt that the USSR would start to try to take more and more if the US did not stop them in Cuba. For all of these reasons, the Cuban Missile Crisis happened.
The main effect of this crisis was to scare both sides. Both sides realized that they had come very close to war over the issue and they realized that such a war had to be avoided. This encouraged them to compromise with each other, to set up direct communications for use in times of crisis, and to be somewhat less aggressive so that they did not come into direct conflict. These were the main effects of the Cuban Missile Crisis.