Third-party payment providers
Shopify supports two different types of credit card payment providers: direct providers and external providers. If you're using a direct provider, your customers can complete their purchases directly on your online store without having to pay at a third-party checkout. If you're using an external provider, your customers must complete their purchases on a checkout page that's hosted outside of your online store.
You can activate or change a payment provider from the Payment providers page of your Shopify admin.