To add additional columns like Discount and Comment in Item section while making PO, follow below steps:

[A] While making Purchase Order in Transactions Module, Click on "Optional Columns" as shown below.

[B] Once you click on the "Optional Columns" a drop-down list appears, you can select either the "Discount" Column or "Comments" columns or both.

[C] Once you select these, it will appear as a column in the Item section.  

Keywords: Discount Columns, Comments Columns