Auto Populate Lists in Excel with Service, Gross, Net and Profit

Hi I hope you had a wonderful weekend, so using the 2016 excel sample attached I was wondering if I could get help with what was previously discussed in the forums threads before. So I wanted on the billing form when the service is chosen it populates the gross, net and profit the only variable that should be changeable is the hours. Want the same services and gross on the invoice. just a question, could you explain a little bit about how you are doing this (functions and/or formulas) so I can look up lessons on how to learn more about this and also for the bill form can I also have the ability to do a drop down with names and how would I add or remove people from that list without ruining the function? Thanks again so much, you are such a lifesaver!