Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research. 

Quick Start Guide to Zotero.  This is a comprehensive guide to Zotero.

(Note: Chromebook users will need to install the desktop program in a specific way.)

The McGill Library has a helpful series of short videos that cover the basics of Zotero.  

If you just want a tool to quickly create a bibliography, check out ZoteroBib.