Connectors allow your web browser to save citations to your Zotero library.
Open Chrome, Safari, or Firefox and click the Zotero Connector link for that browser to install it.
Each browser has its own version of the Zotero connector, so if you use multiple browers you'll need to install each connector.
Using your Zotero login you can access your saved citations and references from any computer on which Zotero is installed.
Syncing works in two parts: data syncing and file syncing. Your citations, along with PDFs, audio, video, images, etc. are saved in the cloud.
To ensure that your Zotero library is being synced with Zotero.org (in the 'cloud'):