Chart comparing features of tools used to manage references includes EndNote, F1000W, Mendeley, and Zotero. Links to guides for each one provides "how to use" information.
The UNC-Chapel Hill University Libraries' Citing Information tutorial introduces you to citing information in a number of citation styles such as APA, MLA, Chicago, and CSE/CBE.
Links to FAQs; a flash tutorial that covers the basics; the Learning Resources section for more in-depth instruction; and the APA style blog; all from the American Psychological Association.
Sample references for the International Committee of Medical Journal Editors (ICMJE) Uniform Requirements for Manuscripts Submitted to Biomedical Journals.