Parent Look-up

I am trying to figure out how to pull other information into a form when 2 forms are linked together. My application is hard to explain but it would be the same way an invoice would work. When you select the name of the item you want to put on the invoice from the drop down list, the rest of the information from the record of the other form is pulled into the invoice. So for example you select the item drop-down list and you choose Battery for example, the cost of the battery is brought into the form also. In another app I used a calculated field. How do I do this in Zoho?

Thanks in advance

Craig