In Marxism theory, the Proletariat were a class of society which did not have ownership in the means of production. Proletarians are wage-workers, who often work for/in; Unsanitary work places, low wages, dangerous situations, often treated cruelly and are the poorest and lowest class who own little or no property.
Within the Marxism Theory, they're is always a constant conflict between the Proletariat and the Bourgeoisie, because (as an example) factory workers were wanting higher wages, but the Bourgeoisie would usually/always turn them down.
According to Marxism, Capitalism is a system based on the fraudulent and under-handed treatment of the proletariat(the "capitalists", those who own and control the means of production). This foul treatment takes place as follows: One- The Proletariat get hired by a capitalist and work for him/her, the workers then produce goods or services. Two- These products or services become the capitalists property, who then sells them to gain profit. Three- a small portion of the wealth produced is used to pay the workers' share (the little they get), while the remaining (surplus value) is dealt amongst the capitalist's (profit). A portion of the Capitalists pay is used to buy supplies, pay bills and add more to their work forces. Therefore the capitalist can earn money from his employees' work, the Capitalists make profit without actually working any labor( excluding the work of hiring, buying supplies and keeping the workers working). Four- THE WORKERS OWN NO MEANS OF PRODUCTION, the proletariat must seek work, even if it means being exploited, just to meet the essentials of life. This is why Marxists argue that capitalists make a profit by exploiting workers/proletariat.
Marx himself urged that the proletariat itself must displace the capitalist system with Socialism, changing the social planning, underpinning the capitalist system, and then developing into a communist society in which: "...the free development of each is the condition for the free development of all" (Communist Manifesto).