From your home screen on select the "Log" button on the top right corner. From the log page, select "Journal Entry", log and save your New Journal Entry. This will show up on your calendar.
In the "log" link in the navigation menu you'll find an option to create a journal entry.
Journal entries are used for posts that are not Crossfit Workouts. For example, you can write a journal entry about how you are changing up your diet or discuss a random athletic activity you've taken part in. They can provide valuable additional information on how CrossFit has affected your life, rather than relying solely on your workout results.
As with any post you make, the journal entry will appear on your Profile calendar for future viewing. The "journals" link in column on the left will store every entry you've ever made.