Citation management systems allow you to download citations from various websites and databases (sometimes with the full-text article), electronically store and organize the citations as well as insert citations and bibliography into your paper in the format of your choice as you write your paper. If you need to manage a large number of citations or are going to need to write a lot of papers that require you to cite sources, a citation management system may make citing sources in your paper a whole lot easier.

Here are some citation management systems you can use:

• Zotero is a free tool that collects, manages, and cites research sources.
• Mendeley is a free reference manager and academic social network.

If you're looking for a lightweight tool just to format individual citations, look at citation generators like ZoteroBib or Noodletools Express.