A simple way to answer your question is to basically tell you the purpose of each product. A primer is normally used to help makeup application last longer, be applied easier and (depending on the product) can help to fill in fine line and wrinkles to create an "even plane" for your makeup. There are many kinds of primers, eye, lip, and foundations are the general 3. Now a foundation concealer or concealer, can be used for many reasons. Generally, clients want their foundation to look natural, therefore, the goal for foundation is to create a look where the entire face is even toned and flawless. Concealer can help to miminize (or completely cover) scars, blemishes, dark spots, birth marks/cosmetic defects, dark under-eyes, etc. Also, many African American suffer from hyperpigmentation, so concealer can be used to help even out the skin tone! Hope this helps you.