Missions guide you through the actions you can take in the game.
To see your current mission, open the MISSION MENU. 
When a mission is completed, you can claim its rewards. 
A new mission will be automatically generated.
Missions are only available for a limited time, and will be replaced if the timer ends.
You can complete a mission and claim the reward right away by spending Tickets.
Check the mission menu often, especially if you are out of things to do.