About Android Apps Analysis

Hello , Dear friends !
I am trying to analyze part of of an Android application codes to find out some way of modification maybe.
The main job shall be de-assembly the code and find out the data file it points to or find out how it processes the data.

There may be some key problems:
1��to find out the main structure of the android app and all its libs
2��to find out the right asm code set to refer to when analyzing the codes
Could you please give me some advice on what tutorial or source to refer to ?

I am a beginner , having only some preliminary knowledge on asm and code analysis from years ago.

Thanks.