Again, please do ensure to enter that discount code when checking out otherwise you could wind up paying more than you need to!
How to use your license key when it arrives:
After payment, the buyer receives an OEM product key to the email specified during registration, which can be activated directly in the Windows 10 system itself.
Head to Start > Settings > System > About the program > Change product key (in this menu you need to enter the received OEM key). The operating system itself, by the way, can be downloaded from the official Microsoft website.
How to upgrade to Windows 11 for free:
Once your genuine copy of Windows 10 is activated, follow the steps here on how to upgrade to Windows 11 from Windows 10 for free.