Here’s how the illustration of my Secret Garden book cover progressed:
I got this question on Tumblr: “Hi I… was wondering if you could talk more about that back to front thing you mentioned? Thx!!!!”
FYI this is using Photoshop CS5, but every version of PS I’ve ever used has had them (Since version 4. Not CS4, 4.). Lots of drawing programs have mask functions, though, so the principles will be the same.