I have a sales receipt which I uploaded now and I just don't know what option to select in Bank/Credit account, whereas in Account/Category I selected Sales.

Hello there, info-design-jr-c. Glad to have you here.

When selecting a bank/credit account, you should choose the one where you want to deposit the customer payments. Also, that's correct that you categorized the sales receipt as Sales/Income. Here's a sample screenshot:

You can check the articles below for  additional reference and guide when organising bank transactions in QBO:

• Categorise and match online bank transactions in QuickBooks Online.
• Reconciling an account. 

Please comment again if you have other questions.  I'm always here to help. Take care always and have a good one!