To add, edit or delete sudo users in putty/bash do the following

1. Type visudo and press enter.
2. Navigate using the arrow keys to where you want to edit.
3. Press insert to enter edit mode.
4. Make your changes. It is very important that you use tabs and spaces correctly.
5. Press esc to exit edit mode.
6. Type :wq and press enter. I remember this command as “write quit”

This is a pretty simple process, but very easy to forget when you only make changes sporadically.