Online Credit Card Payment System Accept Credit/debit Card Payments Online - Do I Understand The System?

Accept credit/debit card payments online - do I understand the system? - online credit card payment system

I `ma web developer and a customer asked me if you can accept payments by credit or debit card on your site.

So I have some research and maybe someone could check whether I `m always such a right.

1.My client needs to obtain a merchant account with the bank.
(this is in conversation with your bank or services are rendered
as worldpay.com (the service I found that knows no boundaries
where would be the company))

2.My Customer must subscribe to a service like payment gateway

3.Possibly online shopping service as payment gateways, which use HTTPS connection.
(HTTPS to the site in question available)

PS
My clients are companies in Latvia.