The main function of a concealer is to hide or offset the shadow under the eyes. It may also be used for elaborate makeup applications and to highlight certain features of the face. Concealers are often used in the area under the eyes because the eyes are set back to the sockets, thus creating a shadow. Also, the eye area has a thinner skin layer which leads to the surface veins becoming more noticeable and prone to discoloration.
For women who are fortunate to have no dark circles under the eyes, they can do away with the use of a concealer. Ideally, the concealer that you buy should match both your natural skin tone as well as the hue of your foundation. You can go one to two shades lighter. Choosing such a concealer will let it blend well with your foundation. Otherwise, you risk creating another color in the areas where the foundation and concealer overlap. A darker colored concealer can be used if the area under your eye has the same color as the rest of your face. Otherwise, you can apply your foundations minus a concealer. This is a very important thing to remember before putting other colors on your face.
Additionally, know that the concealer should be applied before the foundation. Use a pat and blend method in order to ensure that the concealer is applied to the right areas and will not be easily wiped away. After that, apply the foundation lightly on the area where the concealer was first applied and then blend. You can also apply the foundation first and then apply the concealer under your eyes.