The literature review should be the starting point when you begin to think about the topic for your dissertation research. A good literature review presents the context and rationale for your dissertation research. It can help focus your ideas and inspire new thinking. As you undertake your own research a comprehensive literature review will enable you to understand better the scope of the existing research on your topic and to make clear the relationship between previous research and your proposed research.
Literature reviews differ significantly from standard papers or annotated bibliographies and it helps to have a basic understanding of the purpose and process of the literature review before beginning your research.
The video below from North Carolina State University Libraries provides an excellent introduction that I recommend you watch before you begin your literature review project.