> what makes one person work for another

higher income [of goods and services] due to specialization, division of labor and goods/services liquidity.

see: "The Story of Money and Trade" [10min]
https://www.youtube.com/watch?v=QFbHw7VsNlI

Forget about money, think of higher-folded exchanges. A restriction into direct exchanges (the lack of any kind of money) would prevent a tremendous amount of wealth creation: we would spend most of our time working on various basic goods, and when trading would be factually required, we would spend most of our time looking for a trade-want coincidence (I want what you have while you want what I have). To put into perspective, it could take me a couple of decades to buy a telescope from someone with a direct exchange only.

Indirect exchange save us time. Time saved that we can spend with our loved ones, stuff like that. Even without a single type of "money", people engaged in dealing with indirect exchanges (trying to save other people's time) and profiting in return. That's how money emerges: a product for indirect exchange for indirect exchanges, some kind of higher indirect exchange product. And people took the risk of "reaching" such emerged consensus, some must have failed during that process (that exists constantly, even today -- on every single choice anyone make).

Now, money combines perfectly with specialization and division of labor, they enhance each other. Starting from Stewart Mill (I think), each person from a group can be wealthier if that person engage in specialization and trade with others. That's it. If you want to impoverish a subset from a group of people, simply isolate their trading options without their consent. Tariffs etc simply prevent some wealth creation. This is easy to visualize nowadays: isolate a state, or a city, or a neighborhood, or a house, or a person from trading/specializing.

> what is the role of money

So the role of money is to move human effort and resources around towards urgent needs. When some disaster happens, like a tornado, the impacted place suffers from water, for one. The price tends to rise. What is this? That's a toot. It's an alarm trying to ring, signaling to profit-seekers that this is urgent. The higher it is, the more urgent it is. It's like a symptom asking for treatment. A higher water price DOES MAKE water appear in that place rapidly. People will tend to save on their consume, and water from nearby unaffected places will tend to be taken into the affected one, since profit-seekers can make a profit when doing so. (sure, the water may rise a little on areas nearby the affected place, since water would be exported from them and be imported into the affected place) -- and this process would unfold for each next area, until, without a ruler, water would simply arrive into the affected area and the water price would finally be allowed to drop. But that would be because that resource would not be SO urgent.

Now, if I were an evil psycho, I'd simply outlaw water price increase. That's exactly what bureaucrats do.

For this price and coordination thing, see: "What If There Were No Prices? The Railroad Thought Experiment" [6m40] https://www.youtube.com/watch?v=zkPGfTEZ_r4