Exports and Imports: The concept of export and import for any trade system all depends on where you are standing. For example, for goods that are shipped today from China to the United States,
(1) if you were in the United States, you would call these goods "imported from China".
(2) if you were in China, you would call these same goods "exported to the United States".
Import, in from one country or colony to another.
Export, out from one country or colony to another.
Colonial Exports and Imports: In Colonial times, the British government controlled all imports and exports in the New World. The colonists had no voice in the price of their goods or where their goods would be shipped or how much they would be paid for the goods they produced. They had no voice in how much imported goods would cost, or even which goods would be imported. They had no voice in trade. All trade in the New World was controlled back in England with harsh laws and their military to enforce them. This system of trade is called mercantilism.
The triangle trade is simply a term used to signify three major ports of call arranged in such a way that they form a triangle. Via the triangle trade, textiles, rum and manufactured goods were shipped from England to Africa. From Africa, slaves were shipped to the Americas. From the Americas, sugar, tobacco, and cotton were shipped to England. It was a very cost effective way for England to control trade and goods in the Americas for England's benefit. It was not so good for the colonists, though, and especially bad for the slaves.