Bill by bill feature is generally applied on the party ledger, transactions (transaction generally related to cash or credit purchase & sale). Party ledger means Debtors Ledger & Creditors Ledger. Customer or Debtors are who purchase goods or services in credit. Suppliers or creditors are who supply goods & services in credit.

To activate Bill by Bill feature
Gateway of Tally -- press F11 -- Accounting Features
Maintain Bill wise Details =Yes
for Non-Trading A/cs also = Yes

Effect of Bill by Bill feature on Ledger Creation/Alter
Gateway of Tally -- Accounts Info -- Ledger -- Create (in alter already create ledger, select Alter)
Create ledger account (view previous post to learn ledger creation)
Yes the option "MAINTAIN BILL BY BILL"

When you insert any opening balance of debtors/creditors/parties ledger, tally opens Bill by Bill details screen
Here you may put bill by bill data.
Date: - Tally takes closing date of previous year by default because it's opening balance of this year which comes from previous years ending balance. User may change date as per requirement.
Due Dates or Credit Days: - Tally takes closing date of previous year by default. You can change as per requirement. Due dates means, credit allow period.
Name:- Bill name or no.
Adjustment of Non-Billed Amount: - If any non-billed amount are there, these is adjusted this "On Account" balance

Effect of Bill by Bill feature on Voucher Entry/Transaction
Please visit articles on voucher entry/transaction for more details

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