APA is an acronym for the American Psychological Association. The Publication Manual of the American Psychological Association is often used for research work in the social sciences.
These are sites that will help you "build" citations. They're pretty accurate, but be sure to cover your bases by comparing the citations against those in a style manual. Just choose MLA or APA and the type of source you need to create a citation for (a book, a journal article, etc.), and input all of the necessary information.
Ask a librarian if you need additional assistance.