Start the program - you will be asked to activate online
Enter the email address you used to purchase the program and the serial number you received on purchase - if you bought direct from Magix, this will be in the email you received from them, and activate.
Once activated a prompt will come up saying you can download and install the extra content that comes with the software version you purchased.
Go to the Downloads tab top right of the program window and download and install everything - this can take a long while..