I think you have to mount the disk first. This is usually done for you by the DE, which you don’t have at a pure console.
One option (not sure it’s the best) would be to create a permanent entry in /etc/fstab. Currently removable device are mounted dynamically and shown in /etc/mtab only, so they can be mounted on directories under /media named after the disk label.
However if you’re working from a DE console, like konsole in KDE, check the disk directory name under /media and cd to it.
is nonsense. When you want to make /media your working directory
When you want to know what is mounted and where use
You will most probably recocnise where your DVD is mounted (often somewhere within */media *like /media/disk, or /media/<label-of-the-DVD>)
You can then make that you working directory with cd indeed, but there is no need to add in extra / characters at any point.
And brunomcl is correct, musical CDs e.g. contain no filesystem and can not be mounted. Sometimes programs working on musical CDs present the tracks on it as files in a directory, but this is fake, just to make it convenient to work with them.