Communism is a real movement, to achieve dignity for the working class, in a world of alienation. As Friedrich Engels said in his Principles of Communism "Communism is the doctrine of the conditions of the liberation of the proletariat.". It emerged out of the social question, which occurred during the final stages of the process of Modernity, in the form of 19th century Anglo Saxon capitalism.
Communism is related to Socialism, the difference between the two being that Communism is the movement, whole Socialism is the mode of production.
Modernity, particularly in its later stages, comes in the form of the mode of production that is Capitalism. The human being, the worker, was atomized as just another cog in the machine, all of the cultural, social, and traditional, aspects of human life were abstracted into nothing, and world stopped making any sense to humanity. Society was not ruled based on cultural, social, traditional characteristics of each society, which had been the case for thousands of years. Instead society as a whole began to be ruled by the dollar, the need to make profit triumphing over all others at this time. Communism began as a mass movement that would return to the traditions, cultural, and social, aspects of humanity, without compromising the material progress made by modernity. In other words, production would no longer be incompatible with the majority of people's lives. This movement would lead to some kind of mode of production in which we would work for humanity: Socialism.
The original Communist movements at this time had no social science or in-depth analysis of material conditions, but were based on idealism, "If I want something It will happen" the idealist says, despite the fact that real, material, or concrete realities would probably not be able to fit what you "want". Many of these Communist movements believed that we can somehow go from point A to point B, easily. Karl Marx and Friedrich Engels disagreed. They believed that we can't simply go from point A to point B, we can't go from one mode of production to another, simply based on will. They believed that there were (and are) real material forces and contradictions within this world that allow Capitalism to exist the way it does, that leads to it's demise, and to the awakening of a new mode of productions, not ideas, or metaphysics. The science in question, used by Marx and Engels, that allowed them to make such a claim was called Dialectical Materialism. This science, combined with communist or socialist politics is called Scientific Socialism.