i have some to cover under eyes circle, but i can still see them after i apply it on. i probably applied it on wrongly though.

Revlon has really good concealers.
I suggest applying it with a sponge.
Apply an even amount under each eye, and dab evenly with the sponge.
Make sure to apply in the inner corner of the eyes, that is where the biggest shadow hides.
Also, most makeup sponges are available at drugstores.

put moisturizer on before your concealor. This will make it work a lot better and even out you skin tone.

You might have to choose a shade that matches your skin tone more, or a different concealer all togeher (some are more drying than others, and you can see a 'patch' there.
You might also need touse your fingers to blend it out more so even out any harsh lines caused by the concealer.

concealer blends in areas. this is helpful for zits. for your circles..... wear eye popping makeup.....no one will notice

if you want to cover a dark circle or mark, they key is to pat the concealer on that spot, dont rub in like you would with foundation.reason being is because you want the concealer to sit on top of the spot,not rub in and blend. patting is to conceal. blending is to achieve one skintone with flawless skin. you can use a concealer brush or a clean finger. then apply your foundation of choice over it. works for me!

if you can still see them, then you're not putting enough on. Don't cake it on, but put on enough so that you can't see them. Concealer can also be used under foundation, so maybe a light coat of concealer and then apply your foundation. http://www.marykay.com/color/concealers/mksignatureconcealer/default.aspx
above is the link to show the shades I use.
below is a webpage where you can get application tips for applying makeup
http://www.marykay.com/whatsnew/tipstrends/default.aspx