If you use the search bar at the top of this page, I am sure you will find many more in depth threads about each.
Basically a primer is used to prime your face for makeup. Not everyone uses on, nor is it necessary. They are usually gel or liquid form, you use a bit on your face before applying your makeup. Like priming a canvas before you paint. It will help makeup last longer and may reduce redness and the look of pore size, depending on the type you use.
Foundation is in liquid, cream, stick, powder or mousse form. It is a makeup that closely resembles your skin co lour and you use this to cover imperfections and discolorations in the skin. You apply this all over your face to give a smooth, even toned finish. The makeuptalk beauty blog has a post on the different types of foundation and pros of each.
Concealer is like a heavier foundation. It is used to conceal tattoos, pimples, acne, scars, age spots......anything you like really.
I hope this helped you somewhat get a better understanding. /email@example.com 2x" width="20" height="20" />
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.