Different citation styles are used in different disciplines. While English and Art courses tend to use MLA (Modern Language Association) style, History and Humanities courses use Chicago or Chicago/Turabian style and Social Science courses use APA (American Psychological Association) style.
Each citation lists the same item in different ways, using different placement and punctuation, among other things.
The Chicago Manual of Style
A Manual for Writers of Research Papers, Theses, and Dissertations
MLA Handbook for Writers of Research Papers
Little, Brown Essential Handbook
Publication Manual of the American Psychological Association