The left-hand side of the main journal page functions as a quest tracker, telling you what quests have been assigned and what remains to be done on them. The right-hand side of the main journal page shows you the areas you have unlocked. You can click on each one for more information about the people and places in each area. Combat zones that have been "completed" by fighting a sufficient number of enemies in them are marked with a yellow star.
The pages on combat zones provide information about the types of enemies you can encounter there, a meter showing how many of each type of enemy you have encountered and how many remain before the zone is "completed," and when you will reach Milestones when fighting those monsters. (Red squares indicate monsters defeated, grey squares indicate monsters remaining to fight, yellow circles are milestones achieved, grey circles are milestones yet to achieve.)
Clicking on a monster image will give you more information about that monster and its special attacks or defenses.
Your journal will tell you about the major characters that inhabit the Village.
If you hold down the J key while you're on one of the combat zone pages of your journal (except The Forest and Lord Nightmare's Castle) it'll continually refresh with new variations of the regular opponents in that zone.