You can find out how to add payment methods such as payment by credit card to your online shop here.

1. In the menu, select Settings > Payment.
   All payment methods that were already added are displayed. The most important payment methods such as prepayment and payment by invoice are already preset.
2. Select the required payment method from the list box.
   
3. Click Save.

The payment method was added with the Complete it note.

Now set up the payment method so that it can be selected in your online shop (see Setting up Payment Methods).