A site looks up the visitor's IP address in a location database and decides what to serve. It may redirect to a local version, change prices and currency, hide products that are not sold there, or refuse the visit outright.
A proxy with an address in the right country gets the local version. This is the everyday use of geo-targeting: checking adverts, prices and search results as they appear in each market. A site's own terms still apply to how you use what you see.
Read next: Proxies for price monitoring