How to transfer a txt data file to my Android app

Sorry, I stupidly wrote my post in french. Re-writing it in English.

I must transfer a data file necessary for my app.
I read many threads on the subject and I stll don't understand how it works.

1. I'm using android studio 0.8.6. A lot of threads mentions the folder assets which apparently resides in src/main. When I create a new project the folder doesn't exist. I create manually one and I put in it jpg and txt files.

2. I run the following code:
   AssetManager am = getAssets();
   String[] files = new String[0];
   try {
   files = am.list("Files";
   } catch (IOException e) {
   e.printStackTrace();
   }
   for(int i=0;i<files.length;i++){
   Toast.makeText(getApplicationContext(), "File: "+files[i]+" ", Toast.LENGTH_SHORT).show();
   }

And I get a files.length = 0

1. I can create files, write in it and read it but I don know where they reside.

And that's not what I want to do. I want to pass the data with the app.

Sorry for the long email but I'm lost.
Thanks in advance!