Well the difference between the two is very slight, they are almost the same thing (from the computer's perspective).
For example, you have your Windows operating system CD that you just purchased for a hefty sum of $200.00 US. Obviously if that CD were to get damaged... you just lost $200 bucks... Not Good
What you could do is create a backup copy of your disk onto another CD. Now you have a backup (identical copy) of your OS Disk.
Copying would be making a copy of the backup.
This subject has allot of gray area, and definitions will vary but essentially, these are the basic differences of the two.
If your content is already on a computer, for instance a word document, you can create a copy of that file and save it onto a floppy or some sort of removable media. By making your copy.. you have just created your backup.