When you have finally decided (following an initial reading of the literature) on the research question or statement for your research project, you will then begin to read the literature in depth in order to develop your literature review. Do this as soon as possible.
The key concepts, the keywords and phrases in the research statement or question, the conceptual framework for the research project, will indicate the areas within which you should focus your reading for your literature review.
Literature, in the context of the research project, is research that has already been carried out and published.