Gross Domestic Product (GDP) is the total market value of the goods and services a country produces in a given period, usually a year. It is the most common single measure of the size of an economy: a higher GDP means more total output. Because it is a sum of everything produced, it grows with both population and prosperity, which is why it is often read alongside other measures rather than on its own.
GDP per capita divides GDP by population, giving the average output per person. It is a rough proxy for living standards and lets you compare a large country with a small one on a like-for-like basis — a country can have a huge GDP but modest GDP per capita, or the reverse. As an average, it says nothing about how that output is distributed across people.
The trade balance is exports minus imports of goods and services. When a country exports more than it imports it runs a trade surplus; when it imports more it runs a trade deficit. A surplus or deficit is a description of these flows, not a verdict on economic health — countries can grow with either, and the balance shifts with exchange rates, demand and the business cycle.
The current account is the broadest measure of a country’s transactions with the rest of the world. It adds to the trade balance the cross-border flows of income (such as wages and investment returns) and transfers (such as remittances and aid). A current-account deficit means a country is, on net, borrowing from or selling assets to the rest of the world; a surplus means the opposite.