It's important to cite sources you used in your research for several reasons:
You must cite:
Facts, figures, ideas, or other information that is not common knowledge
Ideas, words, theories, or exact language that another person used in other publications
Publications that must be cited include: books, book chapters, articles, web pages, theses, etc.
When in doubt, be safe and cite your source!
EndNote is a software program that allows you to collect and organize all those citations you need when writing your manuscripts. (Other similar programs are Mendeley, Zotero, Reference Manager and Papers. EndNote is the only one supported by Mayo Clinic)
You can import citations from a variety of different online bibliographic databases (PubMed, Ovid, CINAHL) or from publisher's websites. You can import citations from journal articles, book chapters, web pages, legal rules, etc.
It eliminates the arduous task of keying in all that information when you're formatting your bibliography in your word processing program (typically Microsoft Word).