What role did the colonies play in mercantilism and the trans-atlantic trade?

The colonies provided raw goods to their home countries. These goods were refined by the homeland then sold back to the colonies. The colonies were not allowed to refine goods or sell certain expensive/important goods (such as tobacco) to other countries (although this was not enforced very heavily until the late 1700s). So in conclusion, the role the colonies played was to provide economic benefits to their mother country.