To use Zotero, you will need to:
Zotero 5.0 is a downloadable installation that runs in its own window rather than as part of the web browser. It is available for Mac OS, Windows, and Linux. The download includes plugins for GoogleDocs, Word, and LibreOffice.
See the Zotero website for instructions on downloading, installing, and upgrading to Zotero 5.0. If you encounter any problems with installation, the Zotero help forum offers useful advice.
To use Zotero on your mobile device, you can install a "Bookmarklet," a special link that saves items directly to your zotero.org account on the web.
There are a number of third-party apps, developed by groups other than Zotero's team at George Mason, that are aimed at mobile devices. These may allow you to add books by scanning ISBN barcodes, to download and read attachments, and to extract annotations. Zotero maintains a list of these third-party apps on their website.