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. All your computers must be running the same version of Zotero.
First, set up a (free, of course) Zotero.org user account. Then:
Repeat this configuration on each of your computers. Any updates you make on one of your computers will be reflected on the others. This even works to synchronize your library among Windows, Mac and Linux computers.
For more details and help troubleshooting sync problems, check the Zotero site.
Once you create your Zotero.org user account, you can also take advantage of Zotero's collaborative feature, Zotero Groups.
Groups can be private or public, and can have closed or open membership. By joining or creating a Group, you can share references with colleagues and other Zotero users with similar research interests.