I'll try to break it down the way I would for a high schooler, because you seem very confused.
GDP, gross domestic product, is essentially the market value of the aggregate of all goods and services produced in a specific area in a specific period of time. It simply measures the size of an economy.
When someone says, "The United States' GDP in 2019 was $21 trillion", that basically means the United States produced $21 trillion worth of stuff in that given year.
There are a few ways of calculating GDP but the most common ones are the value-added approach, the income approach, and the expenditure approach. The latter is the simplest:
GDP = consumption + investment + government spending + (exports - imports)
Nominal GDP vs GDP (PPP)
So,
Nominal GDP is assessed comparatively by converting the market value of a given country's output to a common currency using current market exchange rates.
GDP (PPP) is nominal GDP with an extra step: in addition to conversion using market exchange rates, GDP (PPP) also takes into account the
purchasing power of the respective currencies.
So nominal GDP is preferable in the context of international economics, whereas GDP (PPP) is preferable when measuring the quality of life in a domestic context, because GDP (PPP) takes into account the cost of living and inflation rates.
per capita
The words
per capita are Latin that translates to "by head", or, in plain English, "per person". Therefore,
GDP per capita refers to
GDP per person.
To obtain GDP (PPP) per capita or GDP (nominal) per capita of a country (or state or territory) is relatively straightforward: you just divide its GDP by its population.
If the United States' nominal GDP in 2018 was $21 trillion, and the population of the United States was 328 million, then the resulting nominal GDP per capita is: $21T/328M = approx. $64,000 per person.
Developmental context
GDP per capita, whether nominal or GDP, is a very commonly used metric of economic development, and to some extent, quality of life. It basically says "
this is how much value the average person in this country creates in a year".
According to the World Bank, the country that topped the list for
nominal GDP per capita in 2018 is Monaco at $185k, which isn't surprising considering it's a very small tax haven for the global richfag elite. For your reference, the United States came in 8th place at $65k, Russia came in 63rd place at $11k, China came in 68th place at $10k, and Afghanistan is near the bottom of the list at $500.
But while GDP per capita is a pretty good measure of economic development, it doesn't take into account economic inequality.
Amongst middle-income countries, I think Brazil and South Africa are pretty prominent examples of this: you have a small group of upper- and upper-middle-class individuals who enjoy a pretty high standard of living, and everyone else is rotting in a slum. Like this, for example:
Chads and Stacies on the left, truecels rotting on the right. Looks like two different countries but isn't.
So economists also look at the Gini coefficient (a measure of inequality), educational attainment, literacy, life expectancy, et cetera -- to gauge a country's level of development.
