This is also a good article about native functions

http://java.sun.com/developer/onlineTraining/Programming/JDCBook/jniexamp.html

helped me a lot ^__^

Hey,

You should read more about JNI (Java Native Interface) which allows you to communicate between your c++ code and your Java code ;)
http://developer.android.com/guide/practices/jni.html (on this link, you got a direct link to the JNI official doc).
Otherwise, you can just try to understand how ImageTargets sample works so that you don't need to read a large amount of docs ;)

Gabriel