What is a style guide?
A handbook or guide that illustrates the accepted format for citing your sources (references) in term papers, theses, articles, etc.
Why should I cite my sources?
Well, mainly, because your professor expects you to (so you won't be accused of plagiarism). That said, citing your sources also shows that you have done research using authoritative sources. Also, bibliographies act as further reading lists and help guide the reader of your paper to additional sources on that particular topic.
Which style should you use?
In many cases, your professor will tell you which style they prefer. If they don't, here's a general break down.
AAA : Anthropology
APA : Business, Education, Psychology, and other Social Sciences
ASA : SociologyChicago (Documentary-Note Style): Literature, History, and the Arts
Chicago (Documentary-Note Style) : Literature, History, and the Arts
Chicago (Author-Date System) : Physical, Natural, and Social SciencesCSE: Science
CSE : Science
MLA : Literature, Arts, and the Humanities
Turabian : History