After you have installed an app, it is automatically added to your store and enabled. Some apps, however, require configuration. First, you should navigate to App Store -> Installed Apps. From here you can Delete, Enable/Disable, or Configure any installed apps. If an app does not have a Configure link, that means the app itself does not require any extra configuration. The shipping and payment apps will now appear as new options on your Shipping and Payment screens respectively. These can now be configured directly from the Shipping or Payment screens.