When you create a PO or PR you can attach special instruction/ Term and condition files/text etc. which you defined under PO setup --> attachment.
You can open this attachment.
steps to be followed :
1) create a PO
2) Go to view --> attachment menu,
3) This will open attchment form.. mention category "to supplier" or "to buyer" as per your requirement.
4) Save it & close attchment form..