This first diagram is one of the first I used when starting to try highlighting and contouring (I am still working and perfecting my technique). As you can see the white areas are where you would apply a highlight. The dark areas are where you put your contour. The dark areas, like below the chin for example, helps to decrease the appearance of a double chin and make the neck look thinner and more defined. Adding contour to the forehead/hair line and temples will help to shadow around that area and create the appearance of a smaller forehead. This is great to do especially when you put your hair up. Adding dark contour to the outside of the bridge of your nose and under the tip will make your nose
look more narrow.
look more narrow.