In Bill management portal - How does the actual bank payment deduction happen?

This is regarding payments initiated in Bill management portal - which results in automatic receipts creation. How does the actual bank payment deduction happen? 

1. When customer enters bank account details - how will that connect to client's bank and how the actual payment happens, does this need any integration with bank?

2. When customer enters credit card details - how will that connect to credit card gateway - does this need any integration as well?  

3. We have existing integrations for credit cards and pre-authorized debit - please advise if we should leverage existing integrations for payments initiated at Bill management portal.