The MLA has a lot of information and tutorials on their website:
Zotero is a free, powerful, easy-to-use research tool that helps you gather, organize, and analyze citations and sources such as pdfs and websites, and then share the results of your research. This personal library of sources can work with your word processing tool to format a paper in your choice of style.
Installation of Zotero
Installation of Browser Connector (Add-on/extension)