Adding a user to sudo group

Open sudo config file
visudo

Go to the end of the file and uncomment %wheel ALL=(ALL) ALL line, it is located about 10 line above from the end of the file.

This change will activate the wheel group, and allow you to add a user to the wheel group (it is like local admin group in windows)
Save the change and close the file

add a user to the wheel group, in this example add a user called test to the wheel group

usermod -a -G wheel test