For each assignment you should refer to your teacher's instructions regarding which citation style to use in your work.
The Purdue Online Writing Lab maintains a rich collection of resources designed to support ethical and effective academic writing. On their site, you can explore their resources for MLA, Chicago, and APA style citations. There are also additional resources for understanding, identifying and avoiding plagiarism and much more.
MLA 9 - Modern Languages Association Handbook, 9th Edition (MLA 9)
Chicago/CMS - Chicago Manual of Style, 17th Edition (Chicago/CMS)
APA - American Psychological Association, 7th Edition
If you have any additional questions about citation, please ask your teacher or a Cox Librarian.