Where am I supposed to type the activation code?

Go To:

[Start] -> [All Programs] -> [StarMessage] -> [Configuration]

This will bring up the configuration screen.

Press the button named [Enter Registration Code].

If such a button does not exist on the main configuration screen, check if the program is already registered (see  above).
If you are using a special edition of the screensaver, download the free trial and then activate it.

Type the code in the entry box. If the box is not visible due special screen resolution that you might have in your computer, simply Paste the code using the keyboard Control-V (you will have to copy the code first from the "thank you" email) and press Ok