Find the promo code on Coupodo.com and click "Reveal Code". In the new window, copy the code via CTRL + C, CMD + C (for Apple products). Choose a product in the e-shop. To the item "Use a discount code/Do you have a discount coupon?" paste the copied code. Done, your discount is applied.
How to use the discount?
Click on "Get Deal", a new page will open where you can buy discount products.