Missions are a feature that will allow you to win League Cups by completing different challenges. You can access the mission list from the main screen, indicated by an open map icon.
The mission list will contain different tasks that you must complete in the game; once you complete them, you will get the number of Cups indicated next to the mission's task.
As you complete tasks, you will need to return to the Missions menu to claim your prize. Once you do, said mission will go away and the countdown to another mission will begin.
Make use of the Missions mode to win more Cups and progress faster in the Leagues; this will allow you to win better prizes every week!