ERP

I everyone, am new to Flutterflow, am building an ERP Web App, but there is no tutorial on this, can anyone help me with a tutorial, I want to build a purchase order function where users can add multiple items to a purchase order, that also auto-generate a purchase order ID (like invoice number) and is subjected to admin approval, just like in the link below

https://stocky.untitledsoft.com/app/quotations/store

I do not want the function of selecting the products from a list of product, but rather the user should enter every data manually