The invisible hand is the idea that people operating based on their own self interest in a market economy will optimize “value” and by doing so will increase human welfare. If a person runs a company which makes something that people are willing to buy, they must want or need that thing, and the person will want to make more of that thing so that they can become richer. They do it out of greed, but the richer they get the more they improve the common weal, as it were.
So even though they aren’t doing what they do because they care about the welfare of others (Adam Smith is very clear about that) operating from greed leads to increase human welfare.
Works, except when it doesn’t.
Descriptive statements describe how the world objectively is. Prescriptive statements describe how the world ought to be.

