APA Style was developed by the American Psychological Association. The standard citation style guidebook for the fields of psychology, business, education, health science, public service, and social science is the Publication Manual of the American Psychological Association, 7th edition, 2019. It is commonly referred to as "The APA Manual".
Two types of citations are included in most research papers: citations within the text of the document and a list of reference citations at the end of the paper.
Purdue University's Online Writing Lab (OWL) is a highly respected source of online writing information. They have many resources, including an APA Formatting and Style Guide.