I'd like to start off by saying that contouring is not for everyone, and it's not necessary at all. Between the influence of drag queens and a certain celebrity, there's been a lot of fuss over contour and highlight in recent years, although it's been around in theatrical circles for a very long time. I thought I'd just explain what it is and show the difference it makes.
Contouring is the act of creating light and shadow on the face. This can mask a double chin, shorten a face, chisel out your cheekbones or narrow your nose. You use a darker shade where there should be shadow (in hollows), and a lighter shade where the more light would hit the face (raised areas).
It's fairly time-consuming and not something I do everyday. Also, as I'm at the very end of the skin colour spectrum, highlighting isn't so affective on me. I pretty much have to use white for it to show up and so quite often do not bother.
Read on for the before and afters.