Hi there, @sashegoli-gmail-.
Allow me to share some details about sales orders.
The sales order is a non-posting transaction that will be given to a customer before the actual sale of the items. This means when you create a sales order, the inventory items you've entered will not be deducted from the number of the available items on hand. You'll have to create an Invoice (posting transaction) to link the Quote or Sales order you've created to successfully subtract the items from the stock on hand.
In this example, I'm using Wood Parquet as the inventory item with 10,000 stock on hand and will create a quote with 1,000 items. Here's how to convert a Quote or Sales order to an Invoice.
Now, when you compare the stock on hand before and after creating an invoice, it shows the difference of 1,000 items. This shows that QuickBooks will automatically make changes on the number of items from the record if it is a posted transaction.
To know more on how to manage quotation to an invoice, you may check out this article: Create partial invoices from a quote.
I've added this article for your future reference in case you want to track specific aspects of your business: Run reports in QuickBooks Online.
I'll be here if you have other questions regarding QuickBooks. Let me know in the comment section. Have a wonderful day and I wish you success in your business.