Your delivery address is the location where the goods you order are to be delivered.
You can specify a Delivery Address for your company under Settings - Company Settings - Company Information.
If your company's delivery address is the same as the invoicing address, simply tick the box Same as above and the information will be copied over from the invoicing address fields.
Your delivery address will then appear automatically in the header of the purchase order you send to your supplier. You can also edit the delivery address directly in the PO if a specific order is to be delivered at a different location for example.