android - How can I add a Geofencing on the Google Map

Question

Here, I just developed a android app, use Google Map v2 API. Not very familiar with Java. What I want to make it come true is that, when I enter the circle, trigger some text. I know that Geofencing API could realize that function, and have read and import the sample. It should be have Intent or reaction when I move in or out, but nothing happened. I'm still not very clear how to do next. So sad.. If some could help me solve that problem? Thank you!