There are four ways in which you can spend money. You can spend your own money on yourself. When you do that, why then you really watch out what you're doing, and you try to get the most for your money.
Then you can spend your own money on somebody else. For example, I buy a birthday present for someone. Well, then I'm not so careful about the content of the present, but I'm very careful about the cost.
Then, I can spend somebody else's money on myself. And if I spend somebody else's money on myself, then I'm sure going to have a good lunch!
Finally, I can spend somebody else's money on somebody else. And if I spend somebody else's money on somebody else, I'm not concerned about how much it is, and I'm not concerned about what I get. And that's government. And that's close to 40% of our national income.
This has applications in many ares of the textbook, and will help you think about how the world around you works.
P.S. Milton Friedman is probably the greatest living economist. He won a Nobel Prize in 1976.