To sync your account from computer to computer and keep a backup of up to 300MB of files available in the cloud for free, follow these steps.
Open Zotero, click the gear icon, and select preferences.
Select Sync, then enter your account credentials.
Sync attachment files (i.e. article PDFs, etc.) in My Library using Zotero and downloading files as needed. If you use shared group libraries, we recommend the same settings. Zotero provides 300MB of free storage per user. If you need additional storage, you may purchase it or you may use one of the suggested WebDAV options.