The trial balance is a report totaling all the debit and credit balances in the nominal ledger, to confirm that the total debits equal the total credits.  Due to the double entry concept of the nominal ledger, debits must equal credits and if they do not, an error has occurred.  The trial balance acts as a self-checking mechanism for detecting such errors.  It is a starting point for the preparation of Balance Sheet and Profit & Loss management accounts, therefore it is important that the trial balance does in fact balance before attempting management accounts as these figures will be used in the reports you create.