Hi LindaA,

Thanks for posting in the Community! Inventory items will increase if you entered a purchased item from a supplier as an expense or bill in QuickBooks Online. Once an inventory item is selected on an invoice or sales receipt, the quantity on hand for that item will be reduced.

Let me guide you on how to set up or add an inventory item in QuickBooks Online.

1. Go to Gear icon and select Products and Services. 
2. Select New and then Inventory. 
3. Enter product details. 
4. Select the Income account ▼ dropdown and find the account you use to track what you sell.
5. From the Expense account ▼ dropdown, select Cost of sales. QuickBooks uses this account to track the cost of products you sell.
6. Select Save and close.

For more detailed information, you can check on these inventory articles:

Set up and track your inventory in QuickBooks Online

Can I track inventory manually in QuickBooks Online?

Feel free to drop a comment below if you have any other questions. Have a great day!