Literature reviews may group research based on:
Not all literature reviews require abstracts, but if your assignment asked for an abstract, your abstract should describe:
The length of the abstract varies based on your professor's requirements, but generally abstracts are between 150 - 250 words.
-From the Writing Center at the University of Wisconsin, Madison
For a literature review, you want to focus on the analysis of your sources, not on a description of your sources or summarizing what they found. One of your goals is to convince the reader that your thesis/research question is a good choice using this analysis of your sources.