auto populate syntax question

auto populate syntax question

my apologies if this has already been explained.  I have two forms and would like to auto populate data from one form to the other but can't figure it out. What I am trying to achieve is have an office address information (input.Street, input.City, input.State) from "FORM A" auto-populate onto FORM B after the Office Location (input.office) is chosen from a lookup (drop down menu).

I have gotten very confused as to the best way to achieve this. I could use some help - I am interested in some tutorials or videos on basic scripting if there are recommendations.

Thanks