First, install both the personal research assistant and Zotero Connector.
The personal research assistant is your library, an application downloaded to your computer. The Zotero connector is an add-on for your browser (Firefox or Chrome recommended). Follow the installation instructions or use their Quick Start Guide for assistance.
Then, sign up for a Zotero account using any email address.
With an account, you will be able to sync your library to Zotero.org and access it from anywhere. You'll also be able to participate in group libraries. Read their terms of service and privacy policy.