In order to set up a service in your database, you will need to navigate to the Settings menu, over to the Items column, and then down to the Service page. There, you should be able to double click on a service that you would like to edit. Once the service pop up comes up, you will be able to navigate down to the Pricing Method drop down to select your preferred pricing method (see this article if you need help choosing a method).
If you select Charge Per Unit, it means that you want to be able to enter the qty onto a service line item, and have the service multiply the number you have entered on the service as the charge per unit by the qty.
This option also allows you to enter in a Est Time Per Unit, so that the service will calculate the est hours based on the qty that you enter.