Zotero is a free, open source research tool.  It automatically senses content in your web browser, allowing you to add it to your personal library with a single click.   https://www.zotero.org/

Zotero:

•  collects all your research in a single, searchable interface. You can add PDFs, images, audio and video files
• snapshots of web pages
• organizes your research into collections that act like iTunes playlists
• creates footnotes, endnotes, in-text citations, or bibliographies
• automatically synchronizes your data across as many devices as you choose. Add to your research library on your work PC, and organize your collections on your home laptop. All of your notes, files, and bibliographic data remain seamlessly up to date
• allows you to create and join research groups to focus on any topic you choose.
   

Zotero Documentation Resources are great!

• Tutorials

• Documentation

Is Zotero right for you?  There are other citation management products.  Some free, like Zotero, and some for fee.
Here is a good comparison chart from MIT:  http://libguides.mit.edu/references