IN THE BOOKS OF SELLER :-
debit note :- 
by party a/c debit ----xxx
   to sales a/c--------------xxx
   to  vat a/c---------------xxx

 credit note:-
 BY SALES A/C  debit -----XXX
 BY VAT   A/C  DEBIT -----XXX
    TO PARTY A/C CR--------------XXX
in the books of purchaser the journal entry opposite

Credit Note: Seller

 ( E.g) When we give any discount or  sale return )

          Discount Allowed/Sale Return  xxxx ( Dr)
            
                     to  Party Account         xxxxx ( Cr)


  Debit Note : Purchaser

( E.g When he received discount / purchase retrun to seller)

          Party Account     xxxxxx ( Dr)

             to Discount Received/Purchase retunr xxxxx( Cr)

IN THE BOOKS OF SELLER :-

Debitnote :-
 
 party a/c Dr     xxx
      To sales a/c         xxx
      To  vat a/c          xxx
        (Vat payable)
Creditnote:-

  Sales A/C Dr   XXX
  VatA/C    Dr   XXX
  (Vat Receivable) 
    TO  partyA/C           XXX
(Inthe books of purchaser the journal entry is just 
opposite to the seller)