You can activate your windows 10 machine in the following ways :
- You upgraded to Windows 10 for free from an eligible device running a genuine copy of Windows 7 or Windows 8.1. Your Windows 10 will be automatically activated.
- You bought genuine Windows 10 or Windows 10 Pro upgrade from the Windows Store and successfully activated Windows 10 (through internet or telephone).
- You’re a Windows Insider and upgraded to the newest Windows 10 Insider Preview build on an eligible device that was running an activated previous version of Windows and Windows 10 Preview. Windows 10 will remain activated till you are an insider.
- You bought a copy of Windows 10 from an authorized retailer.
- You bought a digital copy of Windows 10 from an authorized retailer.
- You bought a new device running Windows 10.
For more details, visit Microsoft's article on activating Windows 10.