Editing xorg.conf to support a Wacom tablet, and permissions

[Dave M G]

> By default, the *first* user created has administrative privileges, so
> that'd be *your* password. 

That is what I thought was the case. However, whenever I input my
password, I get this response:

su: Authentication failure

I have gone over it a few times to make sure I'm putting in the correct
password.

Is there possibly some other reason why my authentication would fail?

I understand I probably want to use "sudo", but I'd also like to know
why this authentication is failing?

--
Dave M G