To get started, you will need to identify your reasons for starting a journal. One of the most common types of journals, and one that has hit the mainstream in a big way, is a bullet journal.
A bullet journal is designed to be a cross between your typical journal and a planner. The point of a bullet journal is that users can design it to be whatever they want it to be.
A bullet journal requires some creativity. The advantage of a bullet journal is that you get to design your journal pages to meet any need that you want.
If you want to sketch out art ideas, you can get an art journal. There are also traditional journals filled with lined pages. You can even get a gratitude journal for things you are thankful for.
In my opinion, a diary is a specific type of journal, one that is generally used for memory keeping. Diary entries usually outline specific events that happened.