How to build a purchase order module?

💬 General Discussion
1

I want to buid a PO module.

  1. I build a PO module by module builder. It is based on basic sale.
  2. Build a many to many relation between PO and contracts.
  3. build relation between PO and line item
  4. delpoy

several questions are followed.

how to customize the layout with line-item
how to customize the menu, label of lanuage file, and php file :createpo.php on the module contracts

2

I cannot find the button “add product line”