Once you have installed the MasterCard Payment Gateway Services extension, you can then configure it. To configure the extension, you first need to log into your Magento Admin Panel.
In the Magento admin panel, select System > Configuration from the main navigation.
Then click on the 'Payment Methods' option. You will find an option 'Mastercard Hosted Checkout', as shown below:
The Magento 1 module supports the "Hosted Checkout" integration method only.