Some pages are blank so that you can draw, doodle, paste pictures, or construct a map of the interior of your mind.
Other pages are lined with a teeny-tiny version of a great work of literature. That's where you write your thoughts.
A journal is the cheapest form of psychiatry. It's a dear friend who actually won't repeat your secrets. A journal doesn't care how you spell botulism. It won't call the police if you threaten to murder your co-workers. It won't laugh if you share your fantasy of someday winning the Pulitzer and the Nobel Prize on the same day. A journal doesn't mind if it becomes messy, dog-eared, and scribbled as long as it is always within reach.