Using a Kinguin discount code is easy. All you have to do is:
Go to their website, select the games that you want to buy, and put them in the shopping cart. However, if you're using PayPal, you'll need to sign in first.
Next, click on the shopping cart icon at the top right-hand corner of the page.
Once on the page, click on the "Discount Code" box and copy-paste the voucher code.
You'll immediately see the new discounted price.
Then just click on "checkout" and enjoy your purchase.