American Psychological Association (APA) style is used across many academic disciplines, but as its name suggests it is the standard for Psychology and many other social sciences. The full content of the 7th edition APA Style Guide is available on their website.
Purdue's Online Writing Lab (OWL) and Excelsior Online Writing Lab are also excellent sources for information on how to use APA style, including how to format papers, create a bibliography, cite in text, and more.
If you need to delve into the rules that are used to structure the OWL or the Style Guides, check out the source:
Publication Manual of the American Psychological Association - 7th Edition by 