Bills are due […] days after receipt.
QuickBooks default your bills due date to 10 days after receipt. If your bills due on different date for each vendor then leave this field blank. If most or all of your bills due on certain day after the bills date, e.g. 30 days after the bills date, change this field to 30.
Warn about the duplicate bill numbers from the same vendor.
Turn this option on to prevent duplicate payment to the same bills. QuickBooks warns you when you enter the bills the second time that you already entered from the same vendor.
Automatically use credits.
You may have credits available from your vendors in your business, for example, from the returned products to your vendor and your vendor gives you credit instead of refunding money. If you want to use your credits for payment of your bills, turn this option on.
Automatically use discount.
By the same token, you may have discounts from your vendors, for example, as a wholesale customer you are entitled to 10% discount for each purchase of products. If you want to apply your discounts to your bills automatically, turn this option on. Once you enable this option, you will be asked to specify the Default Discount Account from your chart of account. Depending on your business, this account can be cost of goods sold or expense account.