The MLA or Modern Language Association citation style is used mainly by the English, language, and humanities. The MLA handbook gives guidelines on citing sources both in text and in a works cited page. Check with your professor for specific citation criteria they may have in addition to the MLA style guidelines.
The APA citation style is used mainly in the social and behavioral sciences, natural sciences, nursing, communications, education, business, engineering, and other fields. Check with your professor to see which edition you should use as both editions are being used.