International trade is the exchange of goods and services across borders. An export is something a country sells abroad; an import is something it buys from abroad. Aggregate trade figures sum these across all partners, but the underlying data is made of bilateral flows — the value moving from one specific country to another, which datasets such as UN Comtrade record direction by direction.
Bilateral flows rarely balance between any two countries, and that is normal. A country may run a deficit with one trading partner and a surplus with another; what matters for the overall picture is the sum across all partners, not any single pair. Reading a single bilateral gap in isolation can be misleading.
A tariff is a tax a government places on imported goods. Tariffs raise the price of affected imports and are reported as rates (a percentage of value) that vary by product and by trading partner. They are one of several trade-policy tools; this pack describes what a tariff is and how it appears in the data, without taking a position on whether any particular tariff is advisable.
Underlying much trade is the idea of comparative advantage: countries tend to specialize in what they can produce relatively most efficiently and trade for the rest, which can expand the total goods available. This is a high-level economic concept that helps explain patterns of specialization; real trade is also shaped by geography, history, policy, transport costs and many other factors.