Zotero is a standalone program that works together with a browser extension. You should download and install both before getting started.
1. Go to www.zotero.org.
2. Click on the red button "Download Now".
3. Download Zotero 5.0 (Mac version is shown; it's also available for Windows and Linux) for the standalone program and the Word plugin.
4. Install the Chrome Connector (or Firefox or Safari) for the browser extension.
5. Create a free online account. This creates a space for you on the Zotero server and allows you to add or access your references from any computer through the Zotero interface.