A citation helps the reader to find your original information source. It helps you to avoid plagiarism.
A citation style keeps everyone on the same page by sticking to a standardized format.
The Hamline Writing Center is a great place for help!
Visit the Purdue University's Online Writing Lab APA Style pages.
Also,The ACS style guide: Effective communication of scientific information:
print book, Bush Library first floor location: QD8.5 .A25 2006