Outlook's journal is a lot like a diary and contains a record of your daily activities. Unlike a diary, it's somewhat limited to recording specific records, such as email you send and receive, phone calls you make, and documents you work on. Although it does a good job of automatically tracking your usage of Microsoft Office applications, you must record journal entries for other events or applications yourself.
Among the activities you can automatically record in the journal are
Email you send and receive to selected contacts
Task requests and responses
Meeting requests, responses, and cancellations
Telephone calls you initiate to a contact
Office documents you work on
By automatically recording all documents you work on, ...