Zotero is an easy-to-use research tool that helps you gather, organize, and analyze sources and then share the results of your research. You can attache pdf's to your sources, write notes and quotes in an attached file, and create bibliographies for your research papers.
Below are a few links on how to use Zotero:
This is the link to download Zotero. Under "Documentation" you will find a useful guide to it's functionalities.
This is a research guide to Zotero published by a librarian at Georgia State University. It includes detailed instructions on (1) installation, (2) saving citations, (3) creating bibliographies, (4) synching your library, and (5) the video of a 45 minute instruction session on Zotero.