Your "Countries" report shows where in the world your visitors are coming from. You can click on the "details" button to see the full list of countries ranked by the number of visitors. There you can also see the percentage of your total traffic the individual country stands for.
Plausible uses the MaxMind GeoIP database to determine the visitor country based on their IP address. The IP address itself is discarded to make sure we do not store any personal data.