Zotero is a free tool that collects, manages, and cites research sources. It's easy to use and lives in your web browser where you do your work. Zotero can be downloaded as a stand alone version that works with the Chrome, Safari, Firefox, or Edge browsers. In this tutorial I will be using images from an installation of Google Chrome, but other browser versions are very similar. 

Zotero allows you to attach PDFs, notes, and images to your citations, organize them into easily searchable collections for different projects, and create bibliographies using Word (for Mac or Windows) or OpenOffice using any of over 10,000 citation styles. 

References can be added to a Zotero library in many different ways:  directly from databases, journal websites, Google Scholar, or a library's catalog, by reference file import (for example from an EndNote library), by dragging in PDFs from your hard drive, and by entering them manually.