A literature review discusses published information about a particular topic. As a secondary source, it puts your paper in the wider context of the conversation. A literature review is not simply a list of articles about your topic, rather, it summarizes and synthesizes preexisting research to establish the significance of your paper or to provide background for original research.
The key to an effective literature review is that you analyze studies about your topic in relationship to one another to see what the general lines of thought are regarding your topic, what work has already been done, and what questions still remain to be answered. Part of this process will be to evaluate the methodology used in existing studies, and identify both strengths and weaknesses in the works.
The video below by the University of West Florida provides an excellent explanation of literature reviews.