As an economic system, socialism seeks to manage the economy through deliberate and collective social control. Communism, however, seeks to manage both the economy and the society by ensuring that property is owned collectively and that control over the distribution of resources is centralized to achieve both classlessness and statelessness. Under communism, all people are considered equal and are provided for equally, regardless of their contributions to the economy or to society. This is different from socialism, but both socialism and communism are similar in that they seek to prevent many of the ill effects that are sometimes associated with capitalism, such as economic inequality.
Another difference between socialism and communism is that communists assert that both capitalism and private ownership of means of production must be done away with as soon as possible in order to make sure a classless society, the communist ideal, is formed. Socialists, however, see capitalism as a possible part of the ideal state and believe that socialism can exist in a capitalist society. In fact, one of the ideas of socialism is that everyone within the society will benefit from capitalism as much as possible as long as the capitalism is controlled somehow by a centralized planning system.
Finally, another difference between socialism and communism is centered on who controls the structure of economy. Where socialism generally aims to have as many people as possible influence how the economy works, communism seeks to concentrate that number into a smaller amount.
Socialism and Communism are often used interchangeably as they are both in opposition to Capitalism but they are actually two different economic philosophies. Both have been theorized in different versions ranging from libertarian to authoritarian along the social spectrum. Societies having these economic philosophies bear little resemblance to one another if they are on opposite sides of the social spectrum. To add to the confusion many political entities have described themselves as "Socialist" or "Communist" in name, without actually adhering to either in their economic policies. One of the most notable is the Nationalist Socialist German Worker's party which incorporated "Socialist" into their name but actually carried out a mixed policy of privatized and state Capitalism. Another infamous and most commonly cited one was the U.S.S.R., which not only claimed to be Socialist but also claimed to be a Federation of Democratic Republics. In reality that government was an oppressive bureaucracy with a centrally planned state capitalist economy.
Both Socialism and Communism oppose the private ownership of the means of production and the products produced from that capital, ie. Capitalism. Instead Socialism advocates ownership by the workers who use the capital and Communism advocates ownership of capital by the entire community. So in Capitalism an individual or group of individuals would own a factory, all the machines that produce, let's say a car, and all the cars produced. They then hire workers to make the cars and pay them wages that they compete with each other for. Afterwards they sell the cars and keep what they make...