Error - username is not in the sudoers file. This incident will be reported.
Open the file /etc/sudoers, Add following line in it
username ALL=(ALL) ALL
If your username is john, the line should bejohn ALL=(ALL) ALL
If you want to add whole group as sudoers.
%group-name ALL=(ALL) ALL
where % indicates the name is a group.If your group-name is wheel, the line should be
%wheel ALL=(ALL) ALL