Communism vs. Capitalism
Capitalism is based on the idea of voluntary exchange, which allows business to do business with whomever they want. They can shop for their supplies wherever they want and sell their products for whatever price they want. Communism is not based on voluntary exchange and is ultimately controlled by the government. The government controls how business should be run, where they should buy their supplies and how much they should charge for their goods.
Many communist countries have changed their business practices to a "market" or capitalist format, even though the government is still controlled by a single political group. China is an example of this. They are still technically communist and the government controls many things about what people can believe or say, but they now allow businesses to decide how to run their businesses. Clearly voluntary exchange is good in China now. Just look around and see how many things say, "Made in China."
Check out this link to find about exports and imports into the United States.
Communist vs. Capitalist
You can check out a propaganda cartoon that aired in the cold war era. The cartoon attempts to show the difference between communism and capitalism.