What is a literature review?
A literature review is a "review" of "the literature" on a topic. What does that mean?
So a literature review is a summary of previous research on a topic.
Literature reviews can be a subsection of something bigger or can stand alone:
You may have already written a "research paper" that was really a literature review! Many "library research" assignments are actually simplified literature reviews. So you've probably done one before and you shouldn't be intimidated!
Literature reviews are different depending what their purpose is. If the literature review is part of a Ph.D. dissertation, this review will be comprehensive covering all research on the topic. But if the review is part of a smaller research report, you need to cover the major work that has been done on the topic recently, but it is not necessary to try to identify all research on the subject.
When in doubt about your literature review...
There are dozens of techniques for creating a literature review, and they vary by your field of study, the purpose of the review, the topic, and sometimes even the personal preferences of the professor (or Defense Board, or journal Editor in the cases of dissertations or articles you write for publication).