What purpose do colonies serve for the mother country?

The mother country makes money from the colony using a system called mercantilism. Mercantilism is when you buy something for a low price and sell it at a high price. In this case, the colonists would sell furs to the people in the mother country and recieve like a dollar in return and the people in the mother country turns the fur into hats and recieves ten bucks in return.