Facebook turns 15 next month. When I started Facebook, I wasn’t trying to build a global company. I realized you could find almost anything on the internet—music, books, information—except the thing that matters most: people. So I built a service people could use to connect and learn about each other. Over the years, billions have found this useful, and we’ve built more services that people around the world love and use every day.

Recently I’ve heard many questions about our business model, so I want to explain the principles...