What is a referencing style? A set of rules and methods to follow when acknowledging the thoughts, ideas, and works of others.
Which style should I use? Check your unit outline.
How do I apply the style to my work? The library has online guides containing examples of how to reference.
Library guide to Harvard referencing
Cite Them Right by 
Publication Manual of the American Psychological Association by 
APA Manual (Publication manual of the American Psychological Association)