Open the Flights menu and find the flight you'd like to learn about.
 
 
 
Then tap "Read more" and see the statistics about the particular destination. In this example, Cyprus.
 

 
You can see the all-time statistics and track how many flights are left to get the next star.
 
Please note that the 4th and 5th stars were introduced in version 8.49.09. Only flights completed after updating to this version will count toward earning these stars.