The particular style that your paper should be written in will be determined by your professor, and you should ask her or your TA. If a certain style is not specified, it's probably best to choose one you like and be consistent. (If you aren't sure what a citation style is, it is basically the set of rules which determine how the references should look in the text and at the end of your paper.)
Other style guides are available as well, such as APA, MLA, etc.
If you want more specific help, please contact me.