Default Codification at PO/Vendor/Company level:
For each Vendor and PO you can setup the default Debit and Credit codification accounts. This is what they system will use to code any Accruals/Invoices that come in and are associated to that PO/Vendor. Heirarchy is as follows: PO 1st Vendor 2nd Company 3rd.
To setup the Codification at the Company level go to company settings - See attached screenshot. This will be the default set at the company level.
If desired you can setup defaults at the Vendor and PO level by following similar steps except you would go to the individual element you are looking to apply defaults.