App sending file by email

Hi,
I created an app that take an input from user and save it to file and I need to send this file by email.
File was created in a folder private for application and I need to save it to public (shared) folder.
How can force app to write file in a specific folder ?

I used this sintax:
fos=openFileOutput(FILE_NAME,Context.MODE_PRIVATE);
If I try to put a path before FILE_NAME (such as
"/storage/self/primary/Download/" + FILE_NAME), app crashes.

 

Thanks for answer. I have already inserted this declaration in manifest before sending my post but I didn't write it. When I try to write a txt file in a specific folder, app crashes: it saves file only in app private folder, but in this case I can't use this path to attach file to email.

 

If I don't specify a specific folder, app creates regularly txt file under data/data/com.android.example/memoriainterna2/files where "memoriainterna2" is my app name

 

In this post I attach my Android Manifest and file java for app.

 

Thanks for answer, last friday I posted my Manifest file and also Java file used in my app, could you tell me if there something wrong ?