Citations in graduate school applications
I need to use facts and statistics in my essay. 


You should always indicate the source of your facts and statistics. That means you will need to use citations. Which format to choose? The social sciences typically use APA, MLA, or Chicago Manual of Style. They are very different: MLA uses in-text citations while CMS uses footnotes. Use the one you prefer and be consistent. It helps to make a good first impression, but of course even a perfect mastery of style will not get you accepted. That depends on the quality of your analysis, so focus your efforts on that above all.