Hello, TUSSU.

Yes, the sales receipt is the quickest way to record immediate payment. You can leave the customer field blank if your customer is a stranger. 

Here's how:

1. Click the + New icon.
2. Select Sales receipt.
3. Leave the customer field blank.
4. Enter the sales info, such as the payment method and sales receipt date.
5. Fill in the line item for the product and services you sold.
6. Once done, hit Save and close.

If you want to personalize your sales forms, I've included the following article for a complete guide: Customise invoices, quotes, and sales receipts in QuickBooks Online.

We're always available to help you if you need further assistance in QuickBooks. Have a great day.