All and all, your entire statement is babies.
So if a man needs milk, he has to raise his own cows?
And if he needs medicine, he has to build his own lab?
Or if he needs clothes for his children, he has to grow his own cotton and sew them himself?
Or lets say this, he has a blanket he weaved, but he doesn't need it. He has to trade it for something he does need, lets say milk. He has to trade it to the man who produces milk. Simple enough.
But what if he doesn't need a blanket? The man with the blanket is stuff out of luck. Unless of course he could sell the blanket he made to somebody who needs one for MONEY. Then he can give the MONEY to the milk man, and the milk man can use the MONEY to buy what he needs.
And as bisjac said, any time you trade something it takes on the role of currency.
It's pretty obvious you have no loving clue what you're talking about.