Debits and credits are the main part of the accounting system. They are the method used to record business transactions, and keep track of assets and liabilities. Anything that has a monetary value is recorded as a debit or credit, depending on the transaction taking place. In accounting, debits or credits are abbreviated as DR and CR respectively.
Rules:
Dr: increases asset and decreases liability and owners equity. Eg: if business buys a truck for business use then there in an increase in business asset to a vehicle account
.
Cr: decreases asset and increases liability and owners equity. Using a truck example from the first part, if the business buys a truck for business use , then there in an increase in liability and notes payable account would be increased by the amount of the truck loan.

When recording entries, dr are always entered first. Cr account is listed on the second line.
For every debit there must be a credit.

Trial Balance: a list of closing balance of a ledger accounts on a certain dates and is the first step towards preparation of the Financial Stmts. TB is prepared at the end of the accounting period to assist in the drafting of FS. Ledger balance are segregated in to debit and crdit balance.
Assets are expense account are entered on the debit sideof the trail balance and of TB and liability, capital and income are entered on the credit side of the TB. If all entries are entered correctly the dr and cr will balance.

Purpose of Trial Balance:
First step in the preparation of FS.
TB ensures that all drs and crs are entered in accordance with the double entry concept of the accounting. If the TB do not balance then difference can be investigated and resolved before preparing a financial stmt.
TB ensures that all account balances are extracted from accounting ledger accurately.
TB assist in the identification and