Did you follow the instructions correctly? You entered DISKPART which should bring you to a prompt that looks like this: DISKPART >
At that point you type in: LIST DISK
The message you are getting seems to indicate that you are entering the "LIST DISK" command from a regular command prompt, you need to be at the DISKPART > command prompt.
You should be entering all the commands from the DISKPART > command prompt thru the EXIT command in step 4.
You can certainly follow those instructions to create a bootable USB drive or you could simply download and run a utility called RUFUS that will do it for you.
https://rufus.akeo.ie/