To activate your installation go to the Settings > License menu in the Web Management Console. If you have no valid license, you will only see your installation's Deployment ID. You will also see a warning in the Web Management Console header.
Settings/License page, when no valid license exists
Press the ACTIVATE button to bring up the Activation menu
If you activated your installation, but your license becomes invalid or expired, you will see a RE-ACTIVATE button. After clicking it, the product tries to activate the license with the formerly entered activation information.