Concealer is meant to be worn on top of foundation, or alone. Concealer can be a great tool for mornings when you didn’t get a lot of sleep or could use a little pick me up, but is not really necessary for every day. Concealer is meant to cover the whole under eye area and can be blended with a concealer brush but I feel works better being blended with you fingers (particularly the ring finger) as this applies a little warmth to it and makes it easier to blend. You want to pick a concealer color that is just one shade lighter than your founation to brighten that area a little bit. Also, after applying, pat a pressed power on top of it to make it last and keep it in place.
As for using concealer to cover blemishes, I have always found the to make the problem worse and more noticeable. However, that's just me. my concealer of choice is Bobbi Brown, but I have heard that Covergirl makes good concealer too.
