Style guides and manuals proscribe how to create your citations in a given scholarly community. Three commonly used ones are MLA (used in English courses, for example), APA (used in psychology classes, for example), and Chicago (used in history classes, for example).
Since styles are specific to academic fields, your professor may have you use another style depending on the content of the course.
Below are links to guides and manuals that will help you correctly follow citation styles.