When you pay, you give money in return for something. It’s not always money, though. If your brother says, “You’ll pay for this!” after you snooped in his room, he’s not talking about money. He means you’re going to get it!
Your neighbor might pay you to shovel his driveway — and you can take the money you earn and pay for movie tickets for you and your best friend. Whenever there's an exchange of money and goods (or services), someone pays someone else. It can also be used for ideas. If your teacher warns your class that "crime doesn't pay," she means you might get money but it's not worth it. Education does pay, though, because it makes you smarter.