The cash book
A cash book records all cash and bank transactions in date order, often as a "two-column" cash book (one column for cash, one for bank) or "three-column" (adding a discount column). Unlike most ledger accounts, the cash book serves double duty -- it's both a book of original entry and the actual cash/bank ledger account.
Bank reconciliation
A business's cash book balance for its bank account often differs from the balance shown on the bank statement, due to timing differences -- most commonly unpresented cheques (written and deducted in the cash book, but not yet cashed by the recipient) and uncredited cheques/deposits (received and added in the cash book, but not yet cleared by the bank). A bank reconciliation statement explains these differences to confirm both records are otherwise correct.
Example 1: A cash book shows a bank balance of ₦150,000. The bank statement shows ₦180,000. There is an unpresented cheque of ₦40,000 and an uncredited deposit of ₦10,000. Reconcile the two balances.
Starting from the bank statement balance: -- matching the cash book balance, confirming the reconciliation is correct.