To download McAfee after activation, visit the official website, www.mcafee.com/activate. Start by entering your activation code, which you received after purchasing your McAfee product. Sign in to your McAfee account or create one if you haven't already. Once logged in, choose the device you want to protect, and click on "Download" to start the installation process. Follow the on-screen instructions to complete the installation. If prompted, allow the program to make changes to your device. Once installed, McAfee will automatically update and protect your system from online threats.