Communism and Capitalism are both economic systems, with followers of Communism known as communists and followers of Capitalism known as capitalists.
Put simply, they are polar opposites. Communists want to nationalise all industry, with the economy operating under a system of common ownership which they believe leads to a classless society. In contrast, capitalists believe that it is the private ownership of industry that is most beneficial to society, as this encourages individuals to work hard so they can gain the maximum reward. In so doing, they would see the class system not as an evil - as communists do - but as an incentive for individuals to better themselves.