In mine I would just write down details of how I was feeling, strong emotions or energy imbalances or whatever. Sort of like a mood chart but in much more detail. Could be a simple paragraph or even multiple pages. It's sort of just a way of keeping tabs on the details of your moods as opposed to just the general state of your moods. I think it could be beneficial to do both a chart and a journal. Maybe keep them together so you can mark the general state of your mood on the chart and put the details in your journal.