I assume by “inventory’s” you mean inventory items. Quantities on hand are affected by:
- Purchase invoices
- Sales invoices
- Cash purchases
- Cash sales
- Production orders
Each of these requires that line items on the form be allocated to the correct control accounts so that quantities on hand are adjusted. You do not just go to the Production Orders tab and manually change quantities on hand. Instead, the count is adjusted when any of the listed forms is created or updated.
I suggest reading about all the listed forms as well as inventory-related topics in the Guides: