The best way to define e-commerce is to simply tell you how it works:
One day you were just surfing the Internet as you have done many times in the past when you ran into this web site. You felt like a little kid in a candy store. It has all the electronic gadgets in the world. And you found one of them especially irresistible. You have to have it. After looking it over and reading up on it, you are ready to buy. you clicked on that button that says "click to order" and continued the process.