By default root is locked on Ubuntu for several reasons and
sudo is prefered instead or
gksudo for applications with a GUI.
It can be enabled but I would not recommend it. If you really want to enable root see here but read all the answers first.
Open a terminal CTRL+ALT+T and enter
and enter your password. Inside that terminal you are now root. When you have finished type
exit or just close the terminal and you are back to being you.
Also even as root
/etc/sudoers wont do anything useful its a text file.
If you want to see what is in this file try:
sudo cat /etc/sudoers
And if you want to edit it
In either case you will be asked for a password. This is your login password. When you type there is nothing displayed but it is being accepted just type it and press enter.