In the simplest terms, a VPN creates a secure, encrypted connection—which can be thought of as a tunnel—between your computer and a server operated by the VPN service. In a professional setting, this tunnel effectively makes you part of the company’s network, as if you were physically sitting in the office.
While you’re connected to a VPN, all your network traffic passes through this protected tunnel, and no one—not even your ISP—can see your traffic until it exits the tunnel from the VPN server and enters the public internet. If you make sure to only connect to websites secured with HTTPS, your data will continue to be encrypted even after it leaves the VPN.
Think about it this way: If your car pulls out of your driveway, someone can follow you and see where you are going, how long you are at your destination, and when you are coming back. They might even be able to peek inside your car and learn more about you. With a VPN service, you are essentially driving into a closed parking garage, switching to a different car, and driving out, so that no one who was originally following you knows where you went.
VPN services, while tremendously helpful, are not foolproof. A determined adversary can almost always breach your defenses in one way or another. Using a VPN can’t help if you unwisely download ransomware on a visit to the Dark Web, or if you are tricked into giving up your data to a phishing attack.
What a VPN can do is to protect you against mass data collection and the casual criminal vacuuming up user data for later use. It can also protect your privacy by making it harder for advertisers to figure out who and where you are. That’s why VPNs are important, even when you’re browsing from the comfort and (relative) safety of your home.