Hi there,
Welcome to the QuickBooks Community. I'll be happy to share more info so you can continue to use the program with confidence.
In QBO, all inventory items require an income account and an expense account. When you first set up an inventory item, the system automatically creates an Inventory asset account and a Cost of goods sold account, as these are what the system uses to keep track of the inventory as it moves in and out of your business. When an inventory item is purchased from your supplier, it goes to the inventory asset account. Once that item has been sold to your customer, the expense related to purchasing the item is posted to the COGS account and the income is posted to your selected income account. You can create and use your own COGS accounts aside from the default one if you'd like. You can find further explanation of how the cost of goods and inventory relate to each other in the following Community articles:
Let me know if this info helps. I'll be one message away in case you have other questions.