if you are trying to use google map api v2 for the first time than...follow each and every step of below link carefully.
https://expertsview.wordpress.com/2013/07/05/google-maps-android-api-v2-quick-start-guide/
if you are trying to build on emulator than..
point 3 in above link might be usefull to you
3.Install a compatible version of the Google APIs platform.If you want to test your app on the emulator, expand the directory for Android 4.2.2 (API 17) or a higher version, select Google APIs, and install it. Then create a new AVD with Google APIs as the platform target.Note: Only Android 4.2.2 and higher versions of the Google APIs platform include Google Play services.
Its better to look all the points and setup a working new project.