Password Needed

Hello,
Please i have installed postgresql according to the tutorial in  
http://www.postgresqltutorial.com/ and it was successful installed, i  
have copied the sample database, pagila, but i have problem loading  
the data of the database from command line (windows) after i used the  
command as specified in  
http://www.postgresqltutorial.com/load-postgresql-sample-database/ it  
asked for a password and i gave it the password i used in installing  
postgresql but the password was not authenticated, i also tried using  
my administrator password but it was not also authenticated.
Am a PhD student please what's the right password to use.