Switch over to root and type visudo. The benefit of using visudo is that it will check syntax and whatever else and warn you of any problems you may have introduced into the sudoers file.
visudo shows me that there is a group I could place myself into called 'sudo'. So instead of fooling around in the sudoers file add yourself to the 'sudo' group if you like ... that's what I've done.
%sudo ALL=(ALL) ALL
To add your normal user (tony) to this group:
usermod -a -G sudo tony
The 'tony' user will have to provide his/her password to issue system commands using sudo.