NordVPN sells VPN subscriptions. That means you pay them monthly or yearly to route your internet traffic through their servers, which hides your real location and encrypts what you're doing online. They've got thousands of servers scattered across dozens of countries, so you can pick where you want to appear to be browsing from. The service works on phones, tablets, laptops, and routers. They're not the cheapest VPN out there, but they're reliable and they've been doing this for years without major scandals, which counts for something in a market where trust is basically everything.
Their current offers centre on 2-year commitments at around 68-70% off. That brings the monthly cost down to somewhere around 3 pounds or euros depending on your currency, with 30 days to change your mind if it doesn't suit you. They also do shorter plans if you want to test it out first, but the per-month rate is higher. They've added some extras over the years like threat protection (which you can buy separately with its own discount) and split tunnelling, though none of that is especially unique anymore.
Who buys it? Honestly, a mix. Some people want privacy from their internet provider or networks. Others need to watch content locked to different countries. A few are genuinely concerned about security on public WiFi. Most people probably just want the convenience of not being tracked quite so obviously. NordVPN pitches itself as straightforward and no-nonsense, which is fair, though like any subscription service they'd love you to forget about it after the trial period ends.