The basic principle of Communism is pretty much the same as that of Christianity - to each according to his needs, from each according to his ability. This means that everyone works to the best of their ability and contributes to a common wealth, which is shared out among the population according to their particular needs. Unfortunately, human nature wants to know 'what's in it for me?', which is the basic reason why both Communism and Christianity have failed.
Communism is actually a socioeconomic structure which is based on a classless, stateless society that favors common ownership of the means of production and property. You can find details at the link below: