In order to calculate taxes on billable service work, you can create Tax Codes applicable to your company's locale. These are created at Settings > General Settings > Tax Codes. You can also specify a default tax code that is used as the default for all new Work Orders.
If you plan to use the built-in integration with QuickBooks, you should try to make sure your BlueFolder tax codes match your QuickBooks tax codes as closely as possible. When exporting billing information to QuickBooks, BlueFolder will automatically add tax codes to QuickBooks if they don't already exist.