Mendeley offers word processing plugins for Word and LibreOffice. The plugin adds a Mendeley toolbar to your word processor that allows you to add citations to your document while you write.
When you are ready to add your bibliography to your paper, all you have to do is click on the "Insert Citation"button, add the titles you need, and once you press enter, your citations will be formatted on the the page.
Mendeley offers the most common bibliographic styles such as:
If the style you need is not listed, you can add it by clicking on the "Get More Styles" tab from the Medeley plugin.