The 6th edition of Publication Manual of the American Psychological Association was created by the American Psychological Assocation (APA), and contains the complete guidelines on how to cite research in text as well as formatting of material for publication. It is a set of style rules that condifies the components of scientific writing in order to deliver concise and bias free information to the reader.
Citing Helps Your Reader.
Citing each use of an external source or idea provides a path for the reader to follow in the event that he or she is interested in further reading. It allows the reader to locate the article or book and read the claim in its complete context. During your academic career, your instructor will be your immediate, if not only, reader. Citations perform the same job here as well. A look at some of your sources may help your instructor determine how accurately and effectively you are using your research sources.
Citing Shows Respect.
Just as you would not want others to take and use your ideas and writing without crediting you, you should not take the ideas or writing of others without crediting them. By citing the ideas and writing of writers, you showing them respect and credibility.
Citing Avoids Plagiarism.
It is a fundamental academic requirement that you clearly distinguish your ideas and writing from those of the sources you use in your paper. Citation provides the mode of this distinction. It is in your own self-interest and self-protection to clearly cite your sources in order to avoid severe penalties.
Plagiarism is like the plague.
Here's a quick video from Bainbridge College on how you can avoid it.