The section appears as:
Order Management: If you want the app to manage the orders for you, you can Enable the Setting. If you Enable this, the order when fetched from OnBuy will be sent to your Shopify store so that you can fulfill the order.
If you Disable this setting, the app will not send the orders to your Shopify Store.
Send notification to the customer: If you enable this setting, then as soon as you will be received & fulfill the order from Shopify an notification will sent to customer.