Write 7-15 pages summarizing the literature you found on your topic and your hypotheses. Your literature review should include all the major research on your topic. For instance, if you are researching a new treatment for social anxiety, you need a few articles that explain what social anxiety is, what the research literature says is the best treatment for social anxiety is and why you think another treatment is better with all the research that supports your theory. If you are unsure what a lit review is, a quick google of lit review and a topic would be a good place to start. This should be written in APA style.
Remember, you are planning an experiment as if you have all the resources in the world at your disposal. If you still have questions, please ask.
Use as many sources as you need and cite in APA.