Different disciplines have different citation styles. They tend to include similar elements, such as the title, author, and date, but they have different conventions about the order of the elements, capitalization, etc. These formatting rules serve as a "code" to those familiar with the style so they know a certain number represents the publication date, italics means it's a book title or quotes means it's an article, etc.
The order of the elements also differ from one style to another. For example, in APA style, which is used in many social sciences, the date of the work is listed right after the author's name. In these disciplines, the timeliness of the work tends to be very important. On the other hand, MLA style, used in humanities, the date comes later in the citation because the date of the work is less important.
Often, professors will ask you to use the citation style most commonly used in that discipline. This gives you a taste of what it's like to be in that discipline!
