Zotero is easy to use and can be downloaded as a stand alone version that is compatible with Chrome, Safari, Firefox, or Edge browsers.
Zotero allows you to attach PDF's, notes, and images to your citations, organize sources in a library for various research projects, and create bibliographies using Word or Google Docs.
References can be added to a Zotero library directly from databases, journal websites, Google scholar, or a library's catalog by dragging in PDFs from your hard drive or by entering them manually.
This video tutorial will give you an overview of how to use Zotero.