Very simply, a literature review is a search and evaluation of the available literature in your chosen subject. There are 4 basic objectives:
Doing a literature search requires planning, even simple searches will be better and more focused if you think before doing.
Define your terms. Think about the keywords, spelling, synonyms and how you might connect them. You can find some basic tips in this library guide here.
Search creatively. The library sources are one set of many! You may have access to other libraries (eg: hospital or professional society) as well as the Internet - all of which could extend your search results.
Library is primary! The library resources are purchased to support you. Use the databases, whilst you have access as a member of the University, and don't rely on an internet search engine. The library has subscriptions to some of the key journal resources that are not available for free and can also help 'get' articles from journals that it does not subscribe to.
Obvious versus obscure. If appropriate, don't limit yourself to obvious resources.