The book icon is the portal to your Arendelle Nature Park Guidebook; it keeps mementos from your games. Reindeer you’ve helped will show up in its pages; dishes you’ve cooked will be there, too!
The Nature Park Guidebook also has a page for the pins you have collected. You will collect pins after completing certain criteria in game. There is a steel, bronze, silver, and gold version of each pin. Visit the pin page to see what you have to do to earn them.