Challenges are exercises at the end of the chapter for you to do on your own. Some are easy and provide practice doing the same thing you have done in the chapter. Other challenges are harder and require more problem solving.
We cannot encourage you enough to take on these challenges. Tackling them cements what you have learned, builds confidence in your skills, and bridges the gap between us teaching you Android programming and you being able to do Android programming on your own.
If you get stuck while working on a challenge, take a break and come back to try again fresh. If that does not help, check out the forum for this book at forums.bignerdranch.com. In the forum, you can review questions and solutions that other ...