I'm glad you came in, ms3.
In QuickBooks Online (QBO), you can use the SKU field in the Products and Services set up. SKUs are alpha-numeric-based and usually consist of eight digits which helps keep track of your inventory.
I'll guide you through below:
I've added this tutorial on how to setup Product and Service items in QBO: Adding Products and Services, Customers, and Vendors to Lists.
However, if its the actual bar code that you're referring, this is not yet available in QBO.
While we continue to make improvements with the product, I want you to stay updated with news and product releases by visiting the QuickBooks Blog: https://quickbooks.intuit.com/blog/.
You are always welcome to visit us again if you need help with something else. Have a good one.
You will need an inventory management app with the barcoding feature to integrate with your QBO. You may start exploring from these apps.
If you are a manufacturing company, we may recommend another app.