The players
Four parties: you (the merchant), your customer, a payment gateway, and the banks. The gateway is the safe middleman that moves money and keeps card details out of your hands.
What a gateway does
It takes the payment on a secure page, checks the funds, and confirms the sale to you — so you never touch raw card numbers. That's a feature, not a limitation.
The gateway keeps raw card details out of your hands, so the security burden — and the risk — sits with them, not you.
Settlement takes days
The money doesn't land instantly. Gateways batch and 'settle' funds into your bank account after a day or a few — plan your cash flow around it.
Money settles after a day or a few, not instantly — plan your cash flow around it.