GDP and GDP per capitaboth come from the same underlying number — a country's total economic output — but they answer different questions, and conflating them leads people to wildly overestimate how wealthy individual residents of a "big economy" country actually are.
The difference, precisely
GDP is the total value of everything a country produces in a year. GDP per capita divides that total by population, giving a rough average output per person. A country can rank near the top of the total GDP list purely by having a lot of people, even if each person, on average, produces relatively little.
A huge total economy, a much lower per-person average
India has the 5th-largest GDP in this dataset at $3.91T — but ranks only 133rd of 181 by GDP per capita. A very large population means the same total output translates into a far more modest amount per person than the raw GDP figure alone would suggest.
A small total economy, a very high per-person average
Monaco runs the opposite pattern: 1st highest GDP per capita in this dataset at $288,001, despite ranking only 144th of 181 by total GDP. A smaller population spreads the same (comparatively modest) total output across far fewer people, producing a high average even without an enormous economy overall.
Which one should you look at?
If you're asking "how big is this country's economy in absolute terms" — its weight in global trade, its capacity to fund a military or a large government — total GDP is the right measure. If you're asking "what's it like to live there, economically speaking" — GDP per capita is the far better (though still imperfect) proxy, since it accounts for how many people that output actually has to support.
Figures computed live from this site's GDP and GDP-per-capita datasets (World Bank NY.GDP.MKTP.CD and NY.GDP.PCAP.CD) — see the GDP and GDP per capita pages for full rankings.