The Publication Manual of the American Psychological Association, commonly referred to as APA style, is used by authors in psychology, social sciences, and other disciplines in preparing manuscripts for publication, student papers, theses, and dissertations.
Print copies - TAMU Libraries provides multiple copies of the style manual (see below).
NOTE: APA does not offer an e-book version that libraries can purchase for their collections.
Official apa.org Style Help:
"The OWL" - Online Writing Lab - Purdue University