The STSADM utility is a tool that comes installed with Windows SharePoint Services that allows for a great deal of SharePoint functionality. STSADM can import templates, create sites, change settings, and move data. Unlike backing up and moving data with a program such as FrontPage, STSADM must be run from the server that SharePoint is installed on.
Great caution should be taken when using the STSADM utility because it can perform a myriad of tasks in SharePoint, such as deleting sites and modifying database information. Be sure to test your data migration in a lab setting before running it against a production environment.
To back up a site collection ...