The citations and bibliography in any scholarly work have two purposes:
To do that, your citations and bibliography need to include complete and accurate information about your sources, arranged in a consistent way that does not confuse your reader. At this point in your research, you will all have encountered unhelpful footnotes with mysterious abbreviations, incorrect information, or other problems.
There are many ways to arrange the information. This is called "style" and there are several common styles in use. Commonly used styles in academic writing include The Chicago Manual of Style, MLA, and APA.
An overview and summary of each style is found at Purdue OWL Research and Citation Resources
The full set of rules for each style is found in these publications: