A PO is your internal record of an order placed with a vendor before goods arrive.
Records what you owe the supplier and adds items to your inventory.
Creates a Credit in Accounts Payable and a Debit in Purchases/Inventory and Input VAT accounts.
Increases the Quantity on Hand for all Goods-type items included in the invoice at the specified warehouse.
Use Expenses for overheads that don't involve inventory — e.g., Office Rent, Petrol, Internet, Utilities.