If an order is unscheduled, the order qty is reserved upon order. If an order is scheduled, the order qty is reserved if the shipdate <= today + part leadtime.
At any point in time, qty for an order is also reserved once parts are picked for an order.
Lastly, you can configure Cetec ERP using the config variable, “Reserve Inventory for All Orders,” to reserve the part qty globally upon order entry. This variable is turned off by default in Cetec ERP.