Data entry form - multiple rows

  • I came across this while searching for a solution for creating a complex form:

    It serves my needs, but I have to adapt it a bit and I have no idea how to do it...

    I've attached the file from that site with some comments explaining what I need to do.

    Basically, I need to create a form that feeds a sheet, but automatically creating several rows if one same client buys different products (insert once in the form the client's name and info, choose the several items bought and each product will have its own row, repeating the info about the client).