The Publication Manual of the American Psychological Association, 6th edition, is the ultimate source for using this citation style. Briggs has four copies of the Manual available--two check out and two are kept at the Library Services desk.
When you cite you indicate that information is borrowed from a source. You need to do this every time your borrow information.
Why do you cite?
APA (American Psychological Association) citation style requires you to note in the text of your paper every time you borrow information from a source, whether you quote, paraphrase, or summarize. In-text citations are brief and are used in conjunction with a References list with more complete information about your sources.