Facial contouring is a makeup application technique that is used to accentuate the shape of the face by defining the cheekbones (some also like to contour the nose and along the jawline).
As a makeup artist, I find contouring absolutely essential when completing a face as I believe everyone looks more attractive with more prominent cheekbones and a slender, more defined face. These are the main benefits of facial contouring and with just a little bit of makeup, the face can be dramatically enhanced. The photo above captures a before and after of a face without the facial contours followed by a contoured face (added shadows) as seen along the cheeks, nose, jawline, and forehead.
To achieve this look, you would need to create shadows on the face by picking up a contouring powder (or nowadays cream is another makeup medium available). When choosing a specific contouring product for your face, it is important to pick a shade that is about two shades darker than your natural skintone. If you pick a shade that is too light, it will not create a shadow and just blend in with your face. If you pick something too dark, it will create too harsh of a contrast and look extremely unnatural. I typically stick with contouring powders (I think they are more user friendly and also appear more natural looking than blending creams) and like to use a fluffy brush that is tapered to contour the cheeks. Personally, I use the MAC #138 brush.
Aside from choosing the right shade and makeup medium, it is important to get the placement of the product just right to best accentuate your features. In terms of placement, it is important to apply the contouring product right under the cheekbones as this is what will make them stand out more and create that added definition to the face. Blush would then be applied above the contour in the center of the cheeks, and a highlighter would be applied right above the blush on the very top of the cheekbones at the highest point. Finding the right placement might take some practice so I recommend looking at images in magazines (models and celebrities are always contoured to perfection!) and to go to a professional makeup artist to show you the right products to use along with how and where to apply them on your face.