Don't fret if you're not a writer. Don't feel that you're not creative enough. This isn't a homework assignment, just open up and let it flow. Start with paper. You can buy a blank book at your local book store.
Some people prefer unlined sketch books, so they can draw along with their words.
Or a journal can simply be a steno pad from the stationary store. Buy something small enough to carry around with you so you can write when you're sitting on the sidelines or waiting at the doctor. Journaling doesn't have to be an 'end of the day' thing. It should be handy whenever inspiration strikes. Make a list of the most important people in your life and why they are important.