At the end of every year or (quarterly or maybe even monthly), after completing auditing, you close your books of accounts. This means that you make all your special entries like:
By doing this, your Income and Expense Accounts become zero .You start a new Fiscal Year (or period) with a balanced Balance Sheet and fresh Profit and Loss account.
The Period Closing Voucher will make accounting entries (GL Entry) making all your Income and Expense Accounts zero and transferring the balance to the Account you define.