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.