A payment gateway is a technology used by merchants to accept debit or credit card purchases from customers.
In Moodle 3.10 onwards, payment gateways are used with Enrolment on payment to provide different payment options when purchasing access to a course.
Payment gateways are a plugin type with the PayPal payment gateway included as standard. It is expected that more payment gateways will be developed in the future and shared in the Moodle plugins directory.
Payment gateways are managed via Site administration / Plugins / Payment gateways.
In the PayPal payment gateway settings, you can set a surcharge i.e. an additional percentage charged to users who choose to pay using PayPal.