How can I add lines into my sudoers file?

I have read this answer but don't know how to add the following line into my sudoers file. matthew ALL=(ALL) NOPASSWD: /usr/sbin/service fancontrol start I ran "**sudo visudo**", and a "**/etc/sudoers.tmp**" window popped up. Is "**/etc/sudoers.tmp**" the correct file into which the line should be added? If so, under which line should I add the lines? How can I save it? I cannot find a "Save" option there.

I aim to run "**sudo service fancontrol start**" without a password. GNU nano 2.9.3 /etc/sudoers.tmp # # This file MUST be edited with the 'visudo' command as root.