The term "style" refers to the formatting style that is suggested for the subject for which you are working. The style will dictate how you format not only your citations but also elements such as title pages, outlines, foot notes, page layout, etc.
Typically, in high school, you will either use MLA (Modern Language Association) style or APA (American Psychological Association) style. Always check with your teacher to see what style they wish you to use.
Click here for MLA style resources.
Click here for APA style resources.
As you enter into college and professional careers, it may be necessary to use a more specific style for a given subject area. Click on the pic below to see a prescribed list of styles for certain subject areas that provides links to those formatting styles.