A citation manager is a digital tool that allows you to organize sources, create citations, and form bibliographies. There are several citation managers, some of which are free. Examples of citation managers include RefWords, EndNote, Zotero, and Mendeley. Each of these citation managers has its own advantages and disadvantages, and will suit different needs. See this University of Virginia Library page for a comparison of different citation managers: http://guides.lib.virginia.edu/content.php?pid=562375&sid=4635663.