As you play the game, you can earn more rewards by completing daily, weekly, and monthly challenges. All of them are excellent helpers in the advancement of the game. Please note that completing the weekly tasks may take longer than completing the daily tasks. In the same way, monthly tasks can take even more time than weekly ones. However, it is worth it!
Clicking on the notebook with a clock under your avatar will open a list of these tasks. Please pay attention to the time left before the tasks are updated. You have to complete them within this time frame to get the reward. Otherwise, tasks will be updated.
Good luck!