If you're regularly using more than one computer in your research, Zotero's sync feature can keep your library up to date on all of them.  Zotero can store a copy of your library on the Zotero.org server and check it for updates whenever you open your library on a different computer.

First, set up a (free) Zotero.org user account. Then, open Zotero, and do this:

• From the Edit menu, click on Settings, and then select the Sync tab. 
• Enter your Zotero user name and password.
• Click "Set Up Syncing."

Repeat this configuration on each of your computers.  Any updates you make on one of your computers will be reflected on the others. 

For more details and help troubleshooting problems with syncing, see the Syncing page within Zotero's documentation.