Hi Omar,
That is a great question. A journal entry is generally used to record transactions such as depreciation, amortization or adjustments to income/expense accounts in order to close the books properly. A good rule of thumb for when to record a journal entry is if no other transaction (invoice, bill, credit card payment) can be used then a journal entry may be appropriate. Below are a couple of great resources where you can find additional info regarding journal entries:
https://www.accountingcoach.com/outline
All the Best-
Crystalynn Shelton