The above command is switch user
which when entered with no username will default you to switching to root. Thus if you enter the above and enter the root password you will be switched to root.
This does not relate to sudoers. Adding your username to /etc/sudoers will allow you to run super user commands via the sudo
Thus for example when logged as an ordinary user; you can use sudo to edit the /etc/fstab file which belongs to root.
Say for example you're logged in as john
you can thereafter do the following:
john@mycomputer$ sudo vi /etc/fstab
[sudo] password for john:
You enter your password for the john
user, and you can now edit the file with super user priveleges; provided that john is in the sudoers file.