There are two key elements to Marxist literary criticism. The first is it's attempt to locate literature in its social, economic, and historical context from where is originated. This theory aims to understand how ideas introduced in a work of literature related to values that circulated at the time the work originated. This makes Marxist criticism particularly interesting because it makes a connection between literature and class. The second element in Marxist criticism is that it is a critique of ideology. Ideology is "the ruling ideas of the ruling class." It is used as a way of legitimizing/justifying social and economic arrangements in society that may seem unfair to a certain class because of the fact that they are characterized by inequality. According to the theory of Marxism, ideology has a few natural divisions within it. The final element of Marxism is that it relies upon the presence of social classes in society and the continuous political and economic development of society. Overall these separate elements are put together to create a theory that criticizes different literary works based off of the social and economic standing of the surrounding society at the time of the development of the works.
References
Literary Theory: A Practical Introduction by: Michael Ryan
en.wikipedia.org/wiki/Marxist_literary_criticism