If you charge sales tax, you might have some customers that are exempt from paying sales tax. A setting in each customer's record helps you keep track of this.
Now when you create a sales form for that customer, you can select which tax rate to apply.
If a customer is tax-exempt, don't check this setting. Some tax-exempt customers have a resale number. You can enter it here, if you have one for the customer.
If you charge sales tax to most of your customers, you can set up QuickBooks so that all new customers are taxable.
If you set a default tax rate, and make your customers taxable, QuickBooks automatically selects the default rate for you on sales forms. You can select a different rate for a customer from the Sales Tax dropdown on the form. The next time you create a transaction for that customer, QuickBooks remembers the last rate you used and selects it for you.
A quick way to see your taxable customers is to run the Customer Contact List report. You can do this from Related Tasks in the Sales Tax Center and customize it as needed. The report includes the Taxable field status and the taxable rate.