MacBook Pro asks for a password!!!

Hi!!! I have a question about MacBook Pro password...My cousine bought a MacBook Pro (later 2011) with Lion OS X, she switched it on, and she made all steps that there are, all, instead of to give your password, there was a button "pass" or "go on", i'm not sure...But she clicked on this button. So, after she wanted to instal a application, mac asks her to write a admin password...The quastion is, why it asks for a password, that was not given, and how can she change the password, or to cancel it firstly? Thank you!!!