To export sites from your SharePoint Products and Technologies deployment, you use the following Stsadm command.
Stsadm –o export –url
To back up a site collection, you must use the following stsadm command.
stsadm –o backup –url
To back up an individual database, Web application, or the entire farm, you can use the following Stsadm command.
stsadm –o backup –directory
Restore
To import sites to your SharePoint Products and Technologies deployment, you use the following Stsadm command.
Stsadm –o import –url
To restore a site collection, you must use the following Stsadm command.
stsadm –o restore –url
To restore an entire farm you can use the following Stsadm command.
stsadm –o restore –directory
taken from here