Welcome to the Community, Shin2019.
To record sales, you'll have to enter either an invoice and sales receipt.
When recording sales transaction, make sure to use an inventory item. This will reduce inventory and increase income in the Profit and Loss report.
Let me give you an overview. Once you have a sale that isn't paid yet, you'll have to record an invoice. When your customer pays, enter a payment against that invoice and deposit it to your bank account.
Here's an article to learn more about the accounts receivable workflow:
Accounts Receivable workflows in QuickBooks Desktop. This guide is for Desktop but is also applicable for Online.
It's my pleasure to help, so please let me know if there's anything else I can help you with. I'll always be here to assist. Take care.
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