How to add related data to a layout?

[FileFlipper]

I currently have a layout that contains a portal that shows all the products a customer has purchased. I want to add one new order. In order to select the product for that order I want to click on products to search through existing products. If an existing product does not exist I want the user to be able to add a new product

 

[Fitch]

You might want to start with the invoicing example that comes with FileMaker, or other example files from the Claris site. This is more a scripting question than a layout question -- e.g., a script that takes you to your product layout, perhaps in Find mode, and then... various things depending on your particular vision.