cloning makes an exact bit-for-bit copy onto another drive, whereas imaging makes a compressed image file that you save away somewhere.
so, with cloning you end up with another drive containing the exact same files and folder structure, and with imaging, you end up with one big image file that can be used to make a copy in the future.
use cloning if you buy a new drive and want to copy the old one onto it, use imaging to save a backup.
hope that explains it, if not, let me know!