A journal entry is a record of an accounting transaction. It can be a transfer from one account to another or a full summary of a day's transactions like what we do at bookkeep.com.
Below is an example from QuickBooks. You must choose an account for each line and EITHER a debit or credit amount.
Very important to note that the debits totals MUST match the credits totals or you cannot record the entry. (Read more about a Perfectly Balanced Daily Summary).
This handy graphic should also help with Journal Entries: