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 Zotero.org user account. Then:
Zotero will upload your library to the server.
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.
This section adapted from Jason Puckett's guide through the Georgia State University Library.
If you're working on a library computer, there's another easy option for taking your Zotero library with you.
On the File menu in Zotero, select "Export Library..."
Select one of the file formats you would like to export to. In this case we chose "Zotero RDF" as it is easily re-imported to Zotero at a later date. RDF is also the most versatile when importing to other citation managers.
Zotero is free to use and will store information up to 300MB. If you need more than 300mb, Zotero offers reasonably-priced plans. See the plans here.
You can monitor your storage in your Zotero account. Once you are logged on, select "Settings" at the top o the page, the "Storage." You can monitor your storage and purchase additional storage here.
Note: Like the recycling can in Windows or the trash can on Macs, whenever you "move item to trash" Zotero is just moving it into the trash can. These items remain in the trash (and count as part of your storage) until you empty it.