Welcome to the Apple Support Communities
You have to type your user password.
If you don't remember it, you have to reset the password. If you are using Mac OS X Snow Leopard, see "Resetting your original administrator account password" > http://support.apple.com/kb/HT1274?viewlocale=en_US&locale=en_US
If you are using OS X Lion or Mountain Lion > http://discussions.apple.com/docs/DOC-4101