The best way to find a colour match if you have no idea what to buy is to actually go into the store and have someone match you with a foundation and or a concealer if you need one, this way you don't have to waste money purchasing things that don't work for you. It's a good idea to explain your skin type and specific skin needs such as SPF protection, heavy to light coverage or something for oily or dry skin ect. I know MAC will test out colors and match you, they also give samples so you can take them home and see how the foundation looks in different lighting which I suggest as the store lighting may not always give a reliable first impression.
Sephora also carries many different brands that you could sample as well. And you could also check with whatever makeup suppliers and stores you have in your area.