How work the 5$ discount??

That is correct. When you reach 30$, 5$ discount will be applied in the cart page. In this situation, you would have to pay 26$.

If you buy more than 30$ they automatically take away 5$. So if you buy for 30,01$ you have to pay 25,01$.

ok thanks to you both

Once you've added games that add up to enough in your cart, the discount will automatically be added to the cart so you are able to completely see how everything is calculated before you continue on towards payment.