To allow readers to trace a cited source quickly and accurately, researchers usually follow a certain citation style. These styles are usually outlined in style manuals. A style manual defines whether you should use footnotes, endnotes, or in-text citations. It will also describe the look of your citations--from the order of the elements (author, title, etc.) to spacing and punctuation. These guidelines ensure that your citations are clear to the reader and consistent throughout your work.
The citation style you use depends on a variety of factors. Many disciplines tend to use one particular style over another (APA for psychology, for example). Your instructors may require you use a certain style, so ask what style to use before you begin your research. If you aren't required to use a certain style, use one that you are comfortable with and that best fits your needs. Just follow the guidelines and be consistent.
Below is a helpful video explaining citation styles from Lynda at UChicago, which provides free online and on-demand training for the UChicago community. University of Chicago users must log in to view the complete video.