Citation Managers are tools to help you keep track of your citations as you research and to create/format your citations and bibliography. Both RefWorks and Zotero allow you to keep citations, full text articles, and other research resources organized in one place. You can also use these tools to format your bibliographies and the notes/citations in your papers according to the appropriate style (APA, MLA, Chicago, etc.).
Zotero is a free open source application that works with Firefox, Chrome, and Safari, you can also download a client to your computer. It is a good choice if you use just one computer when researching. You can access citation information when online or offline.
RefWorks is web-based and available only to 7C users. Your data is saved on the RefWorks servers so you must be online to access your citations. So if you use multiple computers you may want to consider this option.