Hi, Now a days there are too many payment gateways that you can use to process cards manually like using Stripe, BrainTree, PayPal etc. And if you want to process card by scanning it then you should use card.io to get Card number and expire date etc. And after getting these details you can process your transactions by using any payment gateway.

For Card.io you can check more here :
https://www.card.io/
https://www.youtube.com/watch?v=7lg0nMH4NFk

If you are using already built payment gateways like PayPal , Authorize.net or Stripe or any other in your Android app or game then they provide there own SDK to integrate with Application.
For example: PayPal gives its own UI page which includes Credit Card form, it directly takes Credit Card values and authorize them and you just have to tell your PayPal account information where the money will be deposited and it also offers card scanning feature.
In Stripe, you can build your own Credit card form or can use theirs.

This way you save complex procedure of payment compliance regulations and the long procedure to acquire bank permission and you don't even have to make a Credit card form in some cases.

But if you want to make your own Payment gateway i.e if you want to be a payment service provider you'll have to communicate with acquiring banks and tell them that you want to build a payment service provider for your firm. And this way all things will be done by you: Credit card form design, authorizing credit cards and you'll have to follow the compliance regulations as per the bank requirements.

You can scan a card with camera by integrating card.io Android SDK.