Hi Yeollie Hnin,
I am Dave, an Independent Advisor, I will help you with this.
1
Are you performing a full clean install from a bootable Windows 10 USB, or are you installing Windows 10 from inside another version of Windows ?
2
Was Windows 10 ever previously installed and activated on your PC?
3
Typically, if Windows 10 was previously installed and activated on the PC, you can clean install Windows 10 from a bootable USB and that will give you the option to skip entering a product key:
Since you previously had Windows 10 installed and activated on that PC during the installation process skip the steps which ask for a product key and select the option 'I am Reinstalling Windows 10 on this PC', and activation will not be an issue, your PC will have a digital entitlement stored on the Microsoft Activation Servers
If you run the installer from inside any version of Windows you will not have the option to skip entering a product key.