If you purchased a basic Keezel, your package does not include a card with an activation code. This means that when your Keezel asks for an activation code, you need to click on Skip this, I'll use basic service for now.
If you purchased one of the Keezel Premium packages (Keezel Premium 1-year, Keezel Premium 2-year, or Keezel Premium Lifelong), there should be a card in the Keezel box with an activation code. The code is made up of 4 strings of 4 characters (letters and numbers) separated by dashes (xxxx - xxxx - xxxx - xxxx). Please fill this code in (the dashes will be added automatically, you don't need to type them) and then click on Activate Premium.