APA is one of the most important citation styles, used not only in Psychology but across all of the social sciences and other disciplines, including: Psychology, Social Work, Business, Marketing, and more.
References are made through in-text, parenthetical notation and a full reference list at the end of the paper.
See a librarian if you need help using this or any citation style.
Purdue University's Online Writing Lab is a popular source for citation help. And unlike the Publication Manual, it's all online.
The Publication Manual is the APA's official reference.