Activation helps verify that Windows hasn't been used on more PCs than the Microsoft Software License Terms allow.
If you see a message that says "Activate Windows," you might need to connect to the Internet or enter a new product key. If you can’t connect, you’ll need to activate Windows by phone.
Swipe in from the right edge of the screen, tap Settings, and then tap Change PC settings.
(If you're using a mouse, point to the lower-right corner of the screen, move the mouse pointer up, click Settings, and then click Change PC settings.)
Tap or click Activate Windows, and then follow the instructions.
If Windows is already activated, you won't see Activate Windows in PC settings.
You can find your key on the box that the Windows DVD came in—or in an email that shows that you bought Windows. It's a 25-character code that looks like this: PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX.
If you don't activate Windows, you'll still be able to use your PC. But you won't be able to change personalization settings, and you'll see messages reminding you to activate.