CNBC star Maria Bartiromo is here to school us on money matters. First, the basics: What's a stock?

"A stock is ownership in a company," Maria says. "You have a friend who is doing well and has a small business and decides, 'I want to take this business to the next level. I need money to do that. I'm going to go public. I want to sell part of that company to the public.' Then a banker comes, they value the business, they divvy it up—shares—and that gives individuals an opportunity to own part of that business."