Trading is a way for many people to make money. For example, I trade forex - it means that I make money on the difference in the price of currencies. I think it would be clearer for you to read about it on this page
http://usforexbrokers.com/who-are-the-us-forex-brokers/, and I'm sure that you won't have any questions after this page, and maybe you'll even decide to become a trader, who knows.