Skill stars mark your success in completing each particular flight. After a specific number of flights, you'll receive a star and a corresponding title:

⭐ One star - Specialist
⭐⭐ Two stars - Master
⭐⭐⭐ Three stars - Expert

⭐⭐⭐⭐ Four starts - Captain

⭐⭐⭐⭐⭐ Five starts - Ace

Each star also grants you an additional reward, and their sum total unlocks new flights for you as you progress.