Can you really make money with ads?

I've heard a lot about people making money through ads, but I'm still skeptical. Can you really make a decent income just by placing ads on your website or social media platforms? How does it work? Do you need a lot of traffic to see any significant returns? And what about the costs associated with running ads - are they worth it in the long run? I'm curious to know if this is a viable option for someone looking to generate some extra income or even start a full-time business.