Note: You can still use Windows without the key, but it'll have some annoying DRM features. Same goes for major updates, like upgrading from Windows 10 to Windows 11.
If you ever need to reinstall Windows, you might need to enter it. Your product key is important for a few reasons. Every Windows computer has its own unique 25-character product key, and it's formatted like this: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX. Your Windows 10 product key is a special receipt that shows you have an 'activated' copy of Windows. But without a receipt, how do you prove that you actually own Windows? Windows 10 is installed thousands of times a day on computers both new and old.
