Check out the Steem White paper. This is popular in digital currency like STEEM and Bitcoin. https://steem.io/SteemWhitePaper.pdf . In Bitcoin, people with computers "mine" bitcoin and process transactions are rewarded with new Bitcoin entering the system. On Steemit, people who post content and interact on the platform are rewarded with new Steem Dollars and Steem Power. Just remember it's all software that runs on a network of computers around the world to keep it secure and fair. Check out this post for a more in detail explanation. https://steemit.com/steem/@steemrollin/steem-where-does-the-money-come-from