When writing a paper information is gathered from many different sources. The information gathered gets incorporated throughout the paper. To indicate that there is substantiated support for what you are saying in your paper, as well as to give credit to the original author of that support, citations are included with the paper. Citations are bibliographic data that enable a reader to find the original piece of work from which information was gathered. In addition to citations, in-text citations point the reader to the proper citation for specific pieces of information in the paper.
Journal Title (these two may be Book Title and Chapter
Article Title Title or Website Name and Webpage Title, etc.)
Year of Publication
There are a few other items depending on what type of source:
Publisher & Location
Volume & Issue Number
URL Where Item Was Retrieved From
Here's an example with the various parts labeled:
Journal Article: Author, A. A., Author, B. B., & Author, C. C. (Year). Title of article. Title of Periodical, volume number(issue number), pages.
Book: Author, A. A. (Year of publication). Title of work: Capital letter also for subtitle. Location: Publisher.
Article in an Online Periodical (including Galileo Databases): Author, A. A., & Author, B. B. (Date of publication). Title of article. Title of Online Periodical, volume number(issue number if available). Retrieved from http://www.someaddress.com/full/url/
The American Psychological Association (APA) provides a method for source documentation that is used in most social sciences courses. The social sciences place emphasis on the date a work was created, so most APA citation involves recording the date of a particular work in the physical text. The date is usually placed immediately after the author’s name in the “References” page at the end of an essay. The most recent APA formatting can be found in the sixth edition of the APA manual.
Book citations in APA generally require author name, publication year, work title, publication city, and publisher.
In APA periodical citation, authors are named by their last name followed by initials; the publication year goes between parentheses and is followed by a period. Only the first word and proper nouns are capitalized for article titles. Periodical titles are written in title case and followed by the volume number, which, with the title, is also italicized.
In APA citation, online sources often include what are known as DOIs, or digital object identifiers. If a DOI is available, it is used in place of a URL. The DOI is a serial number that identifies the source regardless of URL changes, and it can often be found on the first page of an online source. APA generally cites author, date, page title, site title, available page numbers, and a URL or DOI.
Electronic sources in APA format may include a digital object identifier (DOI) number. When a DOI is evident, it may be used in place of a URL address. An online source should include either a DOI or a URL.
For specific examples of each type of citation with their variations see the complete Purdue OWL: Citation Chart.
From: Basics of APA Style Tutorial, apastyle.org