There are many rules when writing papers.  The first is to always give credit where credit is due (that is also probably a quote that needs to be cited, but who said it first?).  These links will give you information about plagiarism and help you to understand if you did it.  If you are questioning if you have plagiarized, you can always go to the Writing Center or go to their website for great resources.

Did I plagiarize?  Check it here!
This site helps you detect plagiarism and improve your writing.   The tool checks your papers for plagiarism, grammar, style and more, and provides detailed explanations of grammar and style errors.  
http://www.grammarly.com/?q=plagiarism

Videos
Avoiding Plagiarism in Research Papers with Paraphrases and Quotations
http://www.youtube.com/watch?v=u1t0G7ZnRG8
Avoiding Plagiarism and Using Proper Citation
http://www.youtube.com/watch?v=N2AR5-sDfbU
Explore what happens when Yavapai College student, Ima Tryin, makes a trip to the Plagiarism Clinic and discovers the importance of citing sources in this tutorial.
http://www.youtube.com/watch?v=n3_tin1ik6E



Websites
Comprehensive website that defines plagiarism, answers frequently asked questions, tells you how to cite sources, and more.
http://www.plagiarism.org/
Understanding Plagiarism:  Click on the “Jump to” menu in the upper left hand corner to access the different sections of this site.
http://wps.prenhall.com/hss_understand_plagiarism_1/6/1668/427064.cw/index.html
Plagiarism and Honor
http://www.english.vt.edu/plagiarism/plagiarism1.html
Purdue Online Writing Lab - Over 200 free resources including writing and teaching writing, research, grammar and mechanics, style guides, ESL (English as a Second Language)
http://owl.english.purdue.edu/