Download the Zotero application and install it on your computer.
Download a Zotero connector for the web browser of your choice. Zotero connectors are available for Firefox, Google Chrome and Safari. For better performance and more features, use Firefox and Google Chrome.
Open the download page with Firefox, it prompts you to install the Firefox connector.
Open the download page with Google Chrome, it prompts you to install the Chrome connector.
Note to Word processor plugin:
When you install Zotero, the Word processor plugin is bundled with Zotero and should be installed automatically.
If you don't see the Zotero tab in Word or are having trouble, go to Zotero -> Preferences -> Cite -> Word Processors, click Reinstall Microsoft Word Add-in button.