Eager to shore up weakening markets and economic data, President Trump has unveiled the first phase of what he calls the “greatest and biggest deal ever made” with China.

More a shaky truce than a final accord, the latest development in the president’s trade war has nonetheless again elevated the murky subject of international commerce to the front pages.

Yet few Americans — including the president — understand how global trade works, both how it can help our economy and how some can be left behind.

Let’s try to unpack a few of the complexities.

For starters, when Mr. Trump talks about the “trade deficit,” he is almost always referring to just imports and exports of physical goods. But international commerce is much more complicated than that. In addition to goods, we trade in services (entertainment and tourism, for example), in which we have a surplus with China and with the world.