Source documents
Every accounting entry starts from a source document, providing evidence of a transaction: an invoice (details of a credit sale/purchase), a receipt (proof of a cash payment received), a credit note (reduces an amount owed, e.g. for returned goods), and a debit note (increases an amount owed, e.g. for an undercharge).
The journal
The journal is the book of original/prime entry, where every transaction is first recorded, in date order, showing which accounts to debit and credit, with a brief narration explaining the transaction.
Example 1: Record the journal entry for a business buying office furniture worth ₦80,000 in cash.
Debit: Furniture account, ₦80,000. Credit: Cash account, ₦80,000. Narration: Being purchase of office furniture for cash.
The ledger
After being recorded in the journal, each transaction is "posted" (transferred) into the ledger -- a collection of individual accounts (like the furniture account, cash account, etc.), each usually shown as a "T-account" with debit entries on the left and credit entries on the right. This grouping by account (rather than by date, as in the journal) makes it easy to see the running balance and full history of any one account.
Example 2: Using the furniture purchase from Example 1, describe how it would appear in the two ledger T-accounts affected.
In the Furniture account, ₦80,000 is entered on the debit (left) side. In the Cash account, ₦80,000 is entered on the credit (right) side -- mirroring the journal entry, now organized within each account's own running record.