This section enables you to arrange the order of the totals in the checkout.
Order Total extensions typically have status and sort order fields. There maybe additional fields depending on the functionality of the order total extension.
Order total status will determine if the order total extension is displayed when checking out.
Sort order determines what order the order total extensions are displayed in.
The sub total of the order is the sum of the price of the product of each order item, each respectively multiplied by the quantity/count value of the order item. The sum is basically the total amount of the order before the shipping charges, discounts, taxes and other relevant values are calculated. Sub-Total is nearly always on the top so the sort order should be the set to the lowest number.
With the discount coupons feature enabled and active discount coupons in your database, a user might apply a discount to an order which will be deducted from the sub total of the order. This field tells you what the total amount of discount is which has been applied for the specified order.
With shipping calculation enabled one or more tangible order items assigned to the order, this value will tell you what the total shipping charge is for the specified order. This value will be added to the sub total of the order and finally presents the total amount of the order as a sum.
The order total is the amount that the user will be/has been charged. The total is the sum of the sub total minus the discount applied, plus the shipping charges, plus taxes. This is the amount for the payment you receive when the user pays via the payment gateway.