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.
Purdue's Online Writing Lab (OWL) is also an excellent source for information on how to use APA style, including how to format papers, create a bibliography, cite in text, and more.
In-text citations in APA use an author-date format. Both paraphrasing and direct quotations require citations, though they can be either parenthetical or narrative. Direct quotations must also include page numbers, if print material.
The purpose of in-text citations is to refer readers to the full citation on the reference page.
APA reference lists must be alphabetical by the last name of the primary author. Multiple works by the same author are listed chronologically.
The general format for reference list citations is:
Article: Last Name, First Initials (Year Published). Article Title. Journal Title, volume(issue), page numbers.
Book: Last Name, First Initials (Year Published). Book Title. Publisher.
More examples and instructions on citing these and other materials can be found on the APA website.