Using it is really simple. Let's say you want to find out if and where you do I/O on the main thread, you'd add the following code in your onCreate:
If the log is not enough for you, you can add additional penalties, like .penaltyDialog (shows a dialog on violations) and .penaltyFlashscreen (only available on newer devices). You can even kill the app: .penaltyDeath (ouch!).
Furthermore, you can set a policy for memory leaks, such as unclosed resources (InputStream, etc):
The same tips as above apply for this policy.
For more tips on improving the performance of your app, see the "Best Practices for Performance", especially "Performance Tips" and "Keeping Your App Responsive".