I'm glad that worked. That means you never had a password set on your Macbook, when you go to install a application. You are prompted for the admin account if there is no password which applies in your case. You leave it blank.
If you wish to apply a password you can do so. However your PC will no longer boot straight to the desktop. Instead you will need to enter the password before doing so.
To add a password click on the Apple logo top left.
choose System Preferences.
From the View menu choose Users & Groups.
Click the lock button if it appears locked; enter the administrator password. Which would be blank
Select your user whose password you want to change.
Click the Reset Password button or the Change Password button.
Enter a new password in both the New Password and Verify fields, and add a Password Hint if desired.
Let me know if you have any further questions.