STSADM

STSADM is a command line tool which we can use to perform administrative tasks on SharePoint Server, this is very powerful since it provides features that are not available in the Central Administration site.
You will be able to find this executable at,
%COMMONPROGRAMFILES%\microsoft shared\web server extensions\12\
For example - C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN

To learn more visit the following TechNet link.
http://technet.microsoft.com/en-us/library/cc261956.aspx
Following link will have the list of operations and properties.
http://technet.microsoft.com/en-us/library/cc263384.aspx