For Guidance follow this link
http://developer.android.com/guide/topics/data/data-storage.html
store file in to the sdcard use this code
private File cacheDir;
if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"/Android/data/YOUR PACKAGE_NAME/files/");
else
cacheDir=context.getCacheDir();
if(!cacheDir.exists())
cacheDir.mkdirs();
}
If you’re using API Level 8 or greater, use getExternalCacheDir() to open a File that represents the external storage directory where you should save cache files. If the user uninstalls your application, these files will be automatically deleted. However, during the life of your application, you should manage these cache files and remove those that aren’t needed in order to preserve file space.
If you’re using API Level 7 or lower, use getExternalStorageDirectory() to open a File that represents the root of the external storage, then write your cache data in the following directory:
/Android/data/package_name/cache/
The package_name is your Java-style package name, such as “com.example.android.app”.
