Zotero is FREE software that allows you to save sources and automatically cite them, with many handy features:
Consult the Zotero Quick Start Guide for tips and videos on how to get started using Zotero. Be sure to download a word processor plugin to make the fullest use of Zotero with Word or other software.
Attend a Zotero Workshop from Columbia University Libraries.
See the Reference & Citation Management research guide for additional tools.
The libraries also provide support for Endnote and Mendeley.
This Guide provides information about which tool to pick.