What is Zotero?
"Zotero [zoh-TAIR-oh] is a free, easy-to-use tool to help you collect, organize, cite, and share your research sources." – www.zotero.org
Zotero has two main forms: an add-on for Mozilla Firefox, and a standalone application. Your saved citations can be archived and shared between copies of the software with an online (free) account on zotero.org.
Zotero is available for Windows, Mac and Linux. There is a Zotero connector add on for Chrome, Safari and Opera browsers (but not for Internet Explorer). Plugins available for Microsoft Word and LibreOffice/OpenOffice/NeoOffice allow you to easily insert citations into your word-processing documents.
Zotero provides a great introduction in its Quick Start Guide.
There are a number of ways to gather citations and put them in your Zotero database
This will only work with documents where the metadata is encoded in the PDF, such as articles downloaded from online journals.