Be careful when editing the sudoers file
This website says: Because improper syntax in the sudoers file can leave you with a system where it is impossible to obtain elevated privileges, it is important to use the visudo command to edit the file.
RIGHT. If you screw up the syntax you may remove access to the system. visudo checks the syntax for you and won't let you save a file with incorrect syntax. It responds to the EDITOR env variable so you can edit it in an editor of your choice.
Another command that helps you edit a resource with safety restrictions is vipw.