The xBees are the experience points you gain in our apps. You earn xBees every time you provide a correct answer in a game. You do not lose your xBees if you provide a wrong answer.
You collect xBees per each course separately. When you start a new course you have 0 xBees.
The xBees cannot be used for buying anything from the app. They just show your experience points for the current course.
How do I earn xBees?