He's asking why money exists, what it represents, people. Money is labor. Your labor is transfered into a universally barterable form, that is what a dollar bill is. Your labor is $8 per hour, or $12 per hour, how however much it may be based on the necessity of the job and the skill you have at performing that function.
Since everyone is not skilled at everything, the requirement to have other people labor for what you want or need arises, at which point you must give these people something in return. You give them your labor in return for theirs, you work for them in return for the work they performed for you.
This became more complex when people started trading cows or food that they labored for for the labor that someone else performed for them.
This something, in the present day, is your labor in the form of money.
Money is labor.
