What is activation?
Activation helps verify that your copy of Windows is genuine and that it has not been used on more computers than the Microsoft Software License Terms allow. In this way, activation helps prevent software counterfeiting. With an activated copy of Windows, you’ll be able to use every Windows feature.
The information collected during activation will not be used to contact you.
It’s required
You have 30 days after installing Windows to activate it online or by telephone. If this 30-day period expires before you complete activation, Windows will stop working. If this happens, you won’t be able to create new files or save changes to existing ones. You can regain full use of your computer by activating your copy of Windows. 
Note: If you choose to automatically activate Windows online, automatic activation will begin trying to activate your copy of Windows three days after you log on for the first time.