Make user a sudoer

If you want to make a normal user to a sudoer first login as an admin.
Open sudoers file with visudo

sudo visudo sudoers

Then fill in the user

username ALL=(ALL) ALL   # Change the user name

Save and exit and done.

You will probably see that this sudoers file will be in quarantine after an os update. Change temporarily to another user with sudo rights:

su admin