Zotero (pronounced "zoh-TAIR-oh") is an application that collects, manages, and cites research sources. It's easy to use, connects with your web browser to download sources, and best of all it's free.
Zotero allows you to attach PDFs, notes and images to your citations, organize them into collections for different projects, and create bibliographies.
This video will show you how to get started:
Zotero Workshop Video: