Some of our librarians have already created a very comprehensive guide to citing your sources. It includes examples of popular citation styles (APA, MLA, etc) and it has sections on citation managers such as Refworks and Endnote Web.
Any time you use someone else's words or ideas, whether you quote, paraphrase, summarize, or otherwise refer to their work, you are required to cite the source.
Things to Cite:
What Does Not Need to be Cited: