Either:
Use the Harvard system of referencing within your text. This will take the form: surname, year of publication, page number, and is enclosed within brackets, for example (Bradley 1998, 277). At the end of your essay you should provide an alphabetical list of all the works you cite
Or:
Use the Numeric System of referencing within your text. At every point in the text where a reference is made, insert a number (in brackets or superscript) and then list the references numerically at the end of your work.