The drive doesn't do much of anything unless you have a disk in the drive.
When your external drive plugged in to your MacBook, click on the Apple menu, and choose About this Mac, and then click on the More Info button.
That should launch the System Profiler.
Click on USB from the list on the left. You should see your external CD drive listed as a USB device.
If you have a disk in the drive, click on the CD drive listing, and you should see information about the disk, too. And, you should see that disk appear on the desktop.
That's assuming that the finder settings are set to show a CD. That might even be turned off in the Finder Preferences.
Serendipity is a lucky guess !