A citation style is the convention established by an entity, such as the American Psychological Association, or an individual author to document material used in writing a research paper, article, thesis, research paper, and so forth. If you use works written by other people to prepare and write your research paper, you must give proper credit to the producers of that information by citing them.
Your instructor will often express a preference for a particular citation style or documentation style, such as APA (The Publication Manual of the American Psychological Association) or MLA (The MLA Handbook for Writers of Research Papers). There are many other documentation styles as well. If your instructor has not indicated preference for a particular documentation style, choose only one style to use throughout your paper.