A journal is a record of what the Word of God is saying to you (as opposed to a diary which often becomes a record of emotions or events over a period of time).

Many people use the SOAP method to journal:
S – Scripture: Read the chapters for the day, looking for one or two verses that particularly catch your attention.  Write the verse(s) out in full.
O – Observation: What do you observe about the passage?
A – Application: How does this passage apply to my life?
P – Prayer: Write your request to God regarding the application of this passage to your life.