Each exchange has its own order book.
So you and I make a decentralized exchangeX. We create a way for people to communicate with each other that they are willing to buy or sell at x price. Those are the makers. And other people can see that and choose offers to take. Miners would be one obvious seller. Anyone who has BTC but has obligations to pay using another asset. People who sell are short, people buy who are long.
Centralized exchanges:
Binance, coinbase
Decentralized exchanges:
Peach bitcoin, hodl hodl, bisq, robosats