After installing Windows 8 Developer Preview it will be activated automatically once you connect to internet, to customize lock screen and to access other Windows settings and features activation is necessary you can activate Windows 8 from metro and classic interfaces.
Activating Windows 8
Before activation, first user need to install drivers for network adaptors that windows failed to install after that create a connection to the internet.
Activating via metro screen
Click on Control Panel icon on Metro Screen to open Metro Control Panel, activation process will begin automatically and let me tell you activation doesn’t takes too long.
Activating via conventional interface
Open desktop Control Panel>System Security>Action Center where for the shown “Activate Windows now (important)” message under Security click on “Go To Windows Activation”
Click on Activate Online in Windows Activation window.
The chances are that your Windows 8 PC automatically activated when you’re online without needing any one of above steps to perform on behalf of you. If activated, you’ll see the below like window.
If Windows asks product key enter the below one.