How to Choose a Style
The first step to writing your citations is choosing a style to follow. Always ask your instructors which style they prefer. As you take classes in different departments though, you'll notice that certain disciplines tend to use certain styles. So, if you're taking an English class, chances are you'll need to use the Modern Language Association (MLA) style. For psychology classes, you'll probably need to use the American Psychological Association (APA) style. Historians tend to use the Chicago Manual of Style's documentary-note style, while economists prefer Chicago's author-date style. Whichever style you choose, be sure to use it consistently throughout your paper.
Also check out style recommendations made by the departments