Citing the work that supports your research is both an ethical issue and a legal issue.
The ethics of citing is based on the scholarly tradition of giving credit for information and ideas that are not one's own. Science has a long tradition of acknowledging priority through citations. You have the ethical responsibility to cite all works that were used to support your research, to give credit to the earlier work and to provide a clear path for those who follow in your footsteps.
As so eloquently expressed by Isaac Newton in a letter to Robert Hooke in 1675 (Merton 1965):
If I have seen further it is by standing on ye sholders of Giants.
The legal issues of citing one's sources are codified in Copyrights, Title 17 of the U.S. Code, which describes the legal protections of authors' and creators' intellectual property rights.
[Merton, RK. 2006. On the shoulders of giants: a Shandean postscript. New York: The Free Press. p. 31]
"There are some actions that can almost unquestionably be labeled plagiarism. Some of these include buying, stealing, or borrowing a paper (including, of course, copying an entire paper or article from the Web); hiring someone to write your paper for you; and copying large sections of text from a source without quotation marks or proper citation.
But then there are actions that are usually in more of a gray area. Some of these include using the words of a source too closely when paraphrasing (where quotation marks should have been used) or building on someone's ideas without citing their spoken or written work."
(From Is It Plagiarism Yet? by the Purdue Online Writing Lab.)
More information is available at Avoiding Plagiarism from the Purdue Online Writing Lab.
Endnote is an application that imports citations from your searches in web databases and helps you organize your references. It works with Microsoft Word helping you create in-text citations, footnotes, and bibliographies.
EndNote Basic (formerly EndNote Web) is an online program that helps you organize references and create properly formatted bibliographies. This is a separate program from the desktop version of EndNote. It is a free version of EndNote available for institutions which subscribe to ISI Databases, like Web of Science.
Mendeley allows you to share references with others or to maintain a private library. Mendeley collections can be exported to Endnote, CiteULike, or Zotero libraries. Mendeley works with Word 2008 and OpenOffice to insert citations into your documents. It enables you to extract citation information from downloaded pdfs.
Zotero is a plug-in from Mozilla that you use with the Firefox browser. Simply download the plug-in, activate the Zotero application by clicking on the Zotero icon in your browser. You can now capture citations into a library held on your hard drive or on a flash drive. Zotero works with Word and OpenOffice after you have downloaded the plug-ins.
APA (American Psychological Association) Style is most commonly used to cite sources within the social sciences.
Common examples using APA style:
Journal Article (Print)
Olson, C. M. (2005) Tracking of food choices across the transition to motherhood. Journal of Nutrition Education and Behavior, 37, 129-136.
Journal Article (Electronic)
Thompson, A. L., & Bentley, M.E. (2013) The critical period of infant feeding for the development of early disparities in obesity. Social Science & Medicine, 97, 288-296. doi:10.1016/j.socscimed.2012.12.007
Kagan, J. (2013) The human spark: The science of human development. New York: Basic Books.
Meyer, D. D. (2013) Family diversity and the rights of parenthood. In L. C. McClain & D. Cere (Eds.), What is parenthood?: Contemporary debates about the family (pp. 124-143). New York: New York University Press.
National Institute of Mental Health. (1990). Clinical training in serious mental illness (DHHS Publication No. ADM 90-1679). Washington, DC: U.S. Government Printing Office.
Report from a Private Organization
American Psychiatric Association. (2000). Practice guidelines for the treatment of patients with eating disorders (2nd ed.). Washington, DC: Author.
Additional examples are given in the guide, APA Style.
Other useful resources
APA Exposed (online tutorial)
This online tutorial from the Harvard Graduate School of Education consists of four modules on APA Formatting Basics, Citing Sources, Reference Citations in the Text, and References. Each module includes examples, explanatory slides with audio and textual narrative, and a quiz.
APA Formatting and Style Guide
From the Online Writing Center at Purdue University, this resource, revised according to the 6th edition, second printing of the APA manual, offers examples for the general format of APA research papers, in-text citations, endnotes/footnotes, and the reference page.