Disk Image or Disk Clone?

ITMA.
​I'm looking to BackUp my whole hard-disk, to 'Image or Clone'. But, which one is the most effective.
So, from the top. Macrium-Free, had a look: scary stuff. I soon realised, that a USB FlashDrive wouldn't have enough capacity. But then, there was an indication, not to use a USB-Stick, because it wouldn't boot the PC. Utilise, a partition; equally, something external ? What to do ? Currently, confused: 'STUCK'.
Any 'Quick-Start' info would be appreciated. The whole 'Manual', looks incredibly confusing.
What I'm looking to do is, have a 'clean' copy, mirror, image, clone; which ever term is correct, most efficacious, to having an alternate, loadable, hard-disk, safely elsewhere. Sorry, to be so diverse; but, it's all a little confusing, and I'd like to get it right, first time.

"It's That Man Again."
The SynicalSurpher. AK.