What we buy and sell includes goods and services. Goods are fairly straight forward. They essential include things produced by the primary and secondary sectors of the economy. The primary sector includes farming, fishing, forestry and mining industries. The secondary sector involves the manufacturing industries.
Services are a little more complex.
Some services are more intangible like banking and management services, engineering and design services as well as the flow of intellectual property royalties. Canada's pattern of trade is dominated by the U.S., both with respect to imports and exports. While our exports flow principally from the primary industries, secondary and tertiary industries are slowly growing as export players. By contrast our imports are dominated by secondary and tertiary sectors. The economic theory of comparative advantage was first developed by David Ricardo of England in the early 19th century.