I do not understand this section in the readme:

Outstanding Payments
-------------------------
Location: Admin > Reports > Orders Awaiting Payment

This report displays all your outstanding payment paperwork. Each radio
button will search for orders that are missing the indicated transaction
piece

What is the "indicated transaction piece" for a regular order (i.e. not a PO)? How does the system know that a COD order is missing its payment?

Overall, I am not figuring this out. And when I search for any overdue payments in my system, I always get nothing.