When you try to do something online, your browser sends a request and with that, it also sends information about you. Nothing that personal, but just general. “I’m from California and I want to watch YouTube” this is so that you can access nearby servers for faster loads instead of servers in India.
A VPN acts as an intermediate. So now you send that request to the VPN host, they ask instead “I’m from Austria and I want to watch YouTube”. Then it just sends the data it received back to you. And you got Austrian YouTube.
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