Zotero can be installed on your desktop or used online in a web browser. To use all of the functions the tool offers, it is suggested to download and install the desktop version.
If you are just looking for a tool to create quick citations, check out Z-bib a simpler citation tool by Zotero.
To use both the desktop version and web version, you first need to create and an account
If you want to use the web version of Zotero, you can log in to your "Web Library" and get started here. For more information go to the Using Zotero section of this guide
One of the benefits of Zotero is that it will sync your files on your desktop to your web library. This also allows you to synchronize your research between devices and protects your from loosing your research if a device dies.
Steps for synchronizing your account after you have installed Zotero
Installing Zotero allows you to integrate the tool with Microsoft Work, Google Docs and OpenOffice for seemless citations. To fully set this up you need to install Zotero and the Zotero Connector. Zotero Connector works best with Firefox and Chrome Web browsers.
If you are using Safari, Zotero Connector is bundled with the desktop installation, you will now need to enable Zotero Connector from Safari Settings Extensions pane.
Installation Video for Windows
Step by Step Installation Video for Mac OS