This feature is applicable for the vendors/bills for which payment terms are defined at vendor record/bill level. This functionality provides the users to get discount from the vendors who pay upfront than the payment terms.
Bill with Payment term as Net 30
Payment terms are defined in accounting lists. At setup level it was defined the discount as 5% if company pays the bill to vendor within 30 days of the bill date.
Discount avail at vendor payment screen
If user make a payment within the 30 days from the bill date, NetSuite automatically shows the discount that the company can get in discount avail field. User can decide upon the amount that can be given by entering the discount in discount taken field. The discount entered in this screen will be posted to the discount account setup in the accounting preferences.