The Journal is where you can unlock more details about the story. After finding all three clues in the five hidden object scenes, you will see a notification on your Journal icon. When you click or tap on it, you will be asked to assemble a puzzle. Once completed, you will receive a gift and an additional story about the chapter. 

For Mobile:
To be able to open your Journal, simply tap on the book icon at the bottom of your screen.

For Computer Users:
To open your Journal, click on the book icon at the bottom right of the screen, above the Play icon.

You do not have to complete the puzzles right away. You can choose to do it at a later stage by opening the Journal and scrolling through the pages.