You need to download an art program (Paint is as crapy as crap gets) and practice on it, until you learn how to do digital art. I use (and so do like..half the population of Digital Artists) Paint Tool SAI, which you can get for free, though it won't be the full version*.
Most people use a Graphic Tablet (like this: www.amazon.co.uk/Wacom-Bamboo-…
, which I have and it is infact really worth it.
Professionals use Photoshop, though that's not necessary to be able to digitalise art.
*The full version is what I use and it is still good.
Hope this helped, SakuraFanLol-chan ^^