purchase order process

The purchase orders are created in ME21N transaction.after the PO is created it is saved in ekko table.this contains all the header data and ekpo has the item data.both tables are linked by field ebeln.ekkn table contains the sales order and purchase order link.from sales order if we need the PO we can use the filed BSTNK.the purchase order document type is F for purchase order and some other thing for purchase requistion.the filed BSART is the document type that is for eg. ZCO for call off PO or Z3PT for release orders.MIGO transaction does the goods receipt for the purchase order.the material document is created after goods receipt is posted.The material document table is MSEG.The material document is MBLNR.