Specifically, how do they work?

Like, how do you know which colors to get? How do you know what goes with your skin tone? How do you even figure out your skin tone in the first place?

And then once you do that, how do you know which kind of product to use on your skin? Powder vs. cream? Blush vs. highlight? How do you learn to put it on?

I'm guessing the answer to most of those is "practice makes perfect," but are there any tips for those of us who are makeup-illiterate? Those of us who are makeup-illiterate and on a budget?