Starting is always the hardest, in my opinion. You will either write from the start or have stage freight, leaving lots of white space. Don't worry though if you're the latter, it's something you build on, a craft. After time you'll naturally rev up that pen in seconds and write write write everything in that wordy brain of yours.
You will create memory-filled pages that evoke healing powers or maybe even laughter. Tears will fall, and thoughts will be pondered. Excitement will grow, and problems will be solved.
Journaling is all about you and how you choose to express your triumphs, failures, or the day-to-day. There isn't a wrong way to journal, and there isn't a wrong time to add substance to your pages.
Some people HATE to write. They avoid it at all costs. Believe it or not, there are ways around writing in a journal and still be journaling. You can color journal, e-journal, or bullet journal your thoughts. Like I said, no wrong way.