A citation style determines the information to include in the citation, the order of the information, the punctuation, and other formatting. Each discipline tends to use one or two citation styles. Always ask your professors which style they prefer.
Frequently-used citation styles:
MLA - Used by many humanities disciplines, including languages and literature
APA - Used by nursing, business, and the social sciences, including psychology, education, sociology, and economics
Chicago / Turabian - Used by history and the arts
CSE - Used by many disciplines in the natural sciences, including biology, geology, chemistry, mathematics, and physics