I know this seems like a stupid question, but do you actually know the difference between concealer and foundation?
If you don't, then you could be using the wrong product for the wrong thing. Which is always frustrating.
Concealer is to literally "conceal" blemishes, scars, dark spots, and dark circles. This should not be spread all over your face. It should only go on areas that need extra coverage, like if you have a zit, for example. it doesn't have to match your skin shade perfectly, either, where a foundation should. In fact, I recommend you go a shade lighter than your actual color for more coverage. This stuff can make your face really white if you put it all over your face, even if you do put powder on afterwards. My personal favorite is Physician's Formula's Conceal Rx.
Foundation is more to even out your skin tone and prime your face for the other makeup that you'll be putting on over it. It helps the makeup stick to your face better. This should be used all over your face and can be put over the concealer if you already have some on. It should match your skin color almost perfectly, and should probably include some SPF for extra protection. I also put it on my eyelids to prime them for eyeshadow. It makes the shadow last longer and prevents some creasing. Again, I like all of the different foundations from Physician's Formula.
Merry Christmas !