You'll receive Quests from various characters throughout the game. These Quests will help you in solving all the mysteries of the Castle.
All active quests will appear at the left of the screen. After you've completed a quest, a green checkmark will appear on the quest.
If you're looking for specific items from a Hidden Object Scene or Zoom Zone, you can tap the "Go To" button under that request to take you directly to the area you need to be in.