Thanks for joining the Community, liz-r-lawrence-g.
 

If you're referring to processing payments for invoices, you can do so from your Receive payment screen.
 

Here's how:
 

1. Use the + New button, then go to Receive payment.
2. Enter your customer's name and their payment date.
3. In the Outstanding Transactions section, choose an open invoice to apply your payment to. For partial payments, change what's in the Payment field.
4. From your Payment method drop-down list, pick Credit Card.
5. Click Enter credit card details and specify the card information. You can also hit Swipe Card. To save a card on file for a customer profile, turn on Use this credit card in the future.
6. Press Save or Use this info.
7. Select Got it, then Save and close or Save and new.

In the event you're looking to process payments for sales receipts, your steps will be a bit different.
 

I've also included a detailed resource about working with payments which may come in handy moving forward: Record invoice payments
 

Please feel welcome to send a reply if there's any additional questions. Have an awesome Monday!