I don't recall either exact command, but I know you can directly ready the CD to a .iso file, that when burned onto a new CD would be a closer duplicate of the original.
Alternately, you can read all the files and directory structure from a CD and form them into a new .iso that may be a functional duplicate of the original but may be a less exact duplicate in many ways. That is also a slower process and more demanding of resources on the computer where you do it.
I expect ncsuapex gave you correct instructions for the second of those two choices. Most likely you would have preferred the first.