Payment Providers allow Tea Commerce to integrate with any number of 3rd party payment gateways such as PayPal, Stripe and Sage Pay.
Out of the box Tea Commerce comes complete with these and many other providers to make it as easy as possible to get up and running.
If you cant't find a Payment Provider for the gateway you wish to use however, you can also write your own too.
The source code for all the Payment Providers is available open source, so if you do want to write your own, they can be used as a great starting point, or if you find a bug in a provider, then it's easy to submit a Pull Request with an update.
The source code for the Paymnet Providers can be found at https://github.com/TeaCommerce/Payment-providers