Reservation settings are available in the menu Company -> Settings -> Modules -> Sales -> Reservations.
Manual only - Reservations can be created in the menu Inventory -> Reservations. A reservation can also be created through an order — after creating the order with the relevant details (company, item), select the Reserve option in the services.
Automatic upon order creation - If an order is created for a quantity greater than what is available in stock, a reservation is created only for the portion that is available in stock. Subsequently, when the goods are received, a reservation for the remaining unfulfilled portion of the order will not be created. The Available quantity will therefore only reflect the originally reserved portion of the order.
Automatic upon order creation and stock receipt - If an order is created for a quantity greater than what is available in stock, a reservation is created only for the portion that is available in stock. Subsequently, when the goods are received, a reservation for the remaining unfulfilled portion of the order will be created. The Available quantity will therefore reflect the entire order.
Automatic upon order creation + Allow reservation into negative - If an order is created for a quantity greater than what is available in stock, a reservation is created for the full quantity of the ordered goods. As a result, the Available quantity will go negative. Subsequently, when the goods are received, the reservation will be fulfilled and the Available quantity will increase. The Available quantity will therefore also reflect the entire order in this case.
__________________________________________________________________
You may also find these helpful