Greetings, jane5.
Welcome to the Community. I'm here to share some insights about the difference between a bill and an expense in QuickBooks Online.
You use a bill when you're going to pay for an expense in a later time. Just like an invoice, you can pay a bill until the reached the due date. While entering expenses work like a receipt that represents something you've already paid.
I'm looking forward to your response about this concern. I'm here anytime you have additional questions. Have a wonderful day ahead.