Go to the main e-mall. Click on one of the levels, then click on the store of your choice, and finally click on "Shop Now"
You can also directly search for your online shop of your choice in the following list by clicking on this button on the right (dynamic text depending on the smartphone or laptop)
Once you are on the merchant's website, let yourself be guided and you will be able to pay by credit card mainly (it is the simplest and the most secure.)
You can also use your debit card, provided it has been activated for ecommerce. Remember to contact your bank to verify that it has been activated for ecommerce.
Note to those who have never paid online on an ecommerce website. It may happen that your bank asks you to authenticate yourself. Just follow the instructions your bank will ask you on the screen often called 3DS or 3D Secure.