Different types of journaling
First and foremost: There is no right or wrong way to journal. Everyone has a different style of journaling and many people switch between them based on how they feel at the moment.
I recently read the book The New Diary by Tristine Rainer. Despite it being from 1978, the ideas have not aged a bit. Mostly because journaling is an activity that persisted for such a long time that humans have figured it out by now.
Tristine Rainer outlines 4 primary methods and 7 more specific methods to journal. I will focus on the 4 primary methods here.
Catharsis
This is a highly emotional type of journaling. You want to get your feelings out. It is common that the diarist jumps from point to point and let his/her emotions dictate the flow.
Description
You write very level-headed and describe a situation or even your day in a more neutral tone. This is the most natural type of journaling for most people and often what you see in media where a person recounts their day. This method also satisfies the urge to preserve memories.
Reflective
The writer takes a step back and tries to learn from the things he writes down or from a situation/event. It can also work well after you already wrote with another journaling method to clear things up or gain insights. The goal is to learn or to give yourself advice. Some people also like to lead a passage with a question to really dive into a feeling or a problem.
Free intuitive writing
In my opinion this is the most challenging or at least the most unfamiliar technique. The diarist tries to let the writing flow without much halt. The goal is to let your inner voices speak and discover what lies beneath the surface. This can look really chaotic from the outside.