Zotero is a free citation management software that is used to collect, organize, cite and store research from all types of sources. It is available on both Windows and Mac computers. Zotero features both a web version that can be used in any internet browser as well as a desktop version. Along with collecting citations, Zotero allows users to attach PDFs, images, screenshots and notes to their citations. Citations in Zotero can be easily organized into different collections for different research projects.
Zotero can be accessed either by logging into Zotero on their website, or by downloading Zotero 5.0, which is a seperate desktop application that connects to the Zotero browser plugin. This plugin, Zotero Connector, works with Chrome, Firefox, and Safari. Zotero Connector can detect what type of source a user is viewing online. Zotero can optionally save a screenshot of an article or webpage sources. Zotero includes plugins for both Word and OpenOffice which allows you to "cite while you write."
For further assistance, check out the official guide on Zotero's website.