Exit/save edit to sudoers file? Putty SSH

Been following instructions for editing sudoers file, made changes but the instructions say to exit using ctrl+x - this just gives me a capital X and a caret. Have tried ctrl:x ctrl+Q Esc.

Not using nano or any other gui (just putty terminal), the change I am trying to save is to set nano as default editor.

I just need to know which keys do I press and in which order?

Also as a side question are there any 'good' linux tutorial sites, I seem to trawl for hours trying to find the simplest answers? 'Good' as in explained well and without omitting vital info (like which gui you are using).

To make changes to sudo from putty/bash:

• Type visudo and press enter.
• Navigate to the place you wish to edit using the up and down arrow keys.
• Press insert to go into editing mode.
• Make your changes - for example: user ALL=(ALL) ALL.
• Note - it matters whether you use tabs or spaces when making changes.
• Once your changes are done press esc to exit editing mode.
• Now type :wq to save and press enter.
• You should now be back at bash.
• Now you can press ctrl + D to exit the session if you wish.