You can get Windows 11 for free if you have a Windows 10 PC with compatible hardware. However if you do not have Windows 10, purchasing a genuine license key is necessary to use Windows 11.

You can buy Windows 11 from Microsoft itself or from authorized resellers ($139 in the US and £119 in the UK for Home Edition, or $199 in the US and £219 in the UK for Pro Edition), or save quite a bit of money by using a key from older version of Windows, such as Windows 7, 8.1 or 10.
Seven years after the release of Windows 10, old Windows 7 keys continue to activate new versions of Windows without problems.
An old Windows 7 DVD or a license sticker from a broken laptop is the best answer to the question “How to get Windows 11 for free”.
You can also buy such keys for much less than the price of Windows 11. Just remember that the versions must match — you can't, for example, activate Windows 11 Pro using a Windows 7 Home key.
If you now want cheap keys (€3.99) you can find them from here. We have been using this site for years without any problems.
