Just to add a little on to what FoxFifth wrote- You're using a Mac, which uses an operating system (or 'OS') called macOS, from Apple. The operating system is what allows you to start your computer and open applications. Other, non-Mac computers will usually use a different operating system, Windows, by Microsoft.
For example, this is what your desktop (what you see when you close all your apps) probably looks like on macOS:

...and this is what Windows 10 looks like:

As for Netflix, my guess is you're trying to download the app onto your Mac. Netflix only has an app for Windows, so that might be where you're confused. However, you can use Netflix just fine without any app by signing in here.