You must install the Zotero Connector in your web browser to begin using Zotero. Once you download Zotero to your computer, you will be prompted to install the Zotero Connector. The default offered is for Chrome. There is a link that offers Zotero Connectors for other browsers.
Once you install the Zotero Connector, the connector icon will appear at the end of your browser address bar. Click on it to add materials to your Zotero Library.