To activate your McAfee product key, start by visiting the official McAfee website www.mcafee.com/activate. Sign in to your McAfee account or create a new one if you don’t have one. Once logged in, find the option to "Redeem your retail card" or "Activate your product." Enter your 25-digit product key, which is typically found on the card or in your purchase confirmation email. Follow the on-screen instructions to complete the activation process. After activation, you can download and install the software on your device to start protecting your system immediately.