You can simply use the Discount % field to apply a discount percentage to the total charges when using Estimate, Invoice, Sales Receipt,Refund Receipt, or Credit Memo.
However, if you are using Invoice Unbilled Activities, automated invoice creation, or if you want to apply a discount to a single charge on a sales transaction form, you can create a special product or service for discounts.
If it's not on the menu, the setting for products and services needs to be turned on. (To turn on: Click the Gear icon > Company Settings (or Account and Settings depending on what you see) > Sales > Products and Services)
QuickBooks translates this into a decimal value (-.10).
If the account doesn't exist, type the name, press Enter, and complete the New Account interview:
If you use a percentage for the Price/Rate, add the discount product or service on a new detail line on the sales transaction form as usual, except in the Qty column, enter the amount of the other charges to be discounted.
For example, if you want to discount charges that total $100, enter 100 in the Qty column for the discount product or service.
When you use a percentage for Price/Rate for a product or service, the amount in its Qty column in the Sales by Product/Service Detail report may not be what you expect. Instead of showing the number of products or services, the Qty column shows the $ amount from which you calculated percentages.