If you're looking for a style like APA, Harvard, etc... just use the search box at the top of the page to search for a style name, or journal title.
If you don't know the name of the style, but know what the final citation should look like, you can use our search by example tool to find styles that most closely match.
If you can't find a style that quite suits your needs, find one that's a pretty close match and click the "Edit style" button to open that style in the visual editor.
Once you've found a style that's suitable for you to use, simply click the "Install" button on the search results, or "Save" a style you've edited, to use it in your reference manager.
Maintainer needed! Development has stalled on these tools since the Mendeley & Columbia University project ended in 2012. The site is visited by over 3,000 people every month and there are plenty of user suggestions and github issues to work on. If you're interested, fork the source code, make your changes, and issue a pull request, I promise to review it.
Steve Ridout, August 2015