you may know Linux operating systems are in the vast majority of cases completely free, and not just free in the sense that you don't have to pay anything, but also in the sense that you're free to legally copy it as many times as you want and share with anyone. What's called illegal piracy in the Windows world pretty much doesn't exist in the Linux world. That's the nature of open source software licensing.
This can lead to money savings because you don't have to buy Windows upgrades to run it legally, and if you're upgrading multiple systems (family, business, etc.) this can add up.
Yet despite being free the quality is surprisingly good. Big companies like Canonical, RedHat, Novell, Google and so on are funding its development and making money on related support services they offer their business users. The model is shown to work. You may not be foreign to open source software if you've used popular programs like Chrome, Firefox, VLC, and many others, all of which are open source, like Linux.