Unless you're uniquely blessed by nature, your face has blemishes and imperfections, like dark spots, scars or dark circles under your eyes. Concealer can make those blemishes fade, if not disappear entirely.
Concealer comes in liquids (good for dry skin), creams and sticks. Liquids are the lightest form of concealer, while sticks are the most solid and opaque.
Concealers also come in a variety of shades, and you want to make sure you find the one (or one palette) that best matches your skin tone. The general guideline is to go one-half to one shade lighter than your skin. A lighter concealer is best for minimizing darker areas--like those circles under your eyes. Darker concealers help hide puffiness.
There are color-correcting concealers, too, which come in green, blue and yellow. Green neutralizes red, so you might use it to mask red spots like scars or acne. Yellow hides bruises well. These work a little differently on different skin tones; for example, people with browner complexions should use peach or orange-colored concealer to hide bluish or grayish splotches on skin.
After you apply concealer, use a sponge to blend it in. Top it off with a light layer of translucent powder to set the stage for a flawless face.