Data syncing merges library items, notes, links, tags, etc.—everything except attachment files—between your local computer and the Zotero servers, allowing you to work with your data from any computer with Zotero installed. It also allows you to view your library online on zotero.org. Data syncing is free, has no storage limit, and can be used without file syncing.
Steps to syncing your Zotero library:
In addition to automatic syncing, you can sync manually at any time by clicking the “Sync with Zotero Server” button on the right-hand side of the Zotero toolbar. By default, Zotero will merge your local Zotero library with your library on zotero.org—any changes you make in one place will be applied to the other and on all other synced computers.