I came from BSD beginings as I stated in one of my earlier posts so I am used to type SU to gain privalidges to make changes that I can't do as a normal user, so the whole "sudo" thing was a lil weird for me and when I typed "su" it asked me for a pass but I hadn't set one so heres how you set a root password.
$ sudo passwd root
Then enter your desired password (different from a normal user account) , the whole point of sudo is to keep people from being logged in as root all the time but need to sudo all the time which is slightly annoying BUT it is deactivated by default for security reasons.
While I am configuring the system is the only time I will use the SU command, NEVER stayed logged in (type exit to quit being a superuser) as you can cause a tremendous amount of damage if you enter the wrong command or you walk away and someone starts playing around where the shouldn't be.
You can also gain "root" by typing: $ sudo -i whichever you choose to use remember to exit and return to a normal user after you have completed your tasks.
IF you forget your password , restart in safemode and in terminal type "passwd" and set a new one.