Files locations - There are several important locations where you can read or write files.
File.DirAssets
The assets folder includes the files that were added with the file manager. These files are read-only. You can not create new files in this folder (which is actually located inside the apk file).
File.DirInternal / File.DirInternalCache
These two folders are stored in the main memory and are private to your application. Other applications cannot access these files.
The cache folder may get deleted by the OS if it needs more space.
File.DirRootExternal
The storage card root folder.
File.DirDefaultExternal
The default folder for your application in the SD card.
The folder is: <storage card>/Android/data/<package>/files
It will be created if required.
Note that calling any of the two above properties will add the EXTERNAL_STORAGE permission to your application.