For assignments, projects and dissertations you will need to do a literature search: find existing literature and information about your chosen topic to use as evidence in support of arguments or points you make.
You may also be asked to produce a literature review: summarising and analysing relevant literature you have found through your research. In a literature review, the literature itself is the main subject of discussion. The aim of a literature review is to show you have identified and examined the key research on a particular topic or question.