From an Android point of view there are an Internal Storage and an External Storage.
1. Internal Storage
In the Internal Storage, the app package is saved:
which can only be accessed with a rooted device.
2. External Storage
The root directory of the External Storage is:
2.1. App-specific directory
In addition, there may be an app-specific directory (which can be created with Taifun’s File extension: https://puravidaapps.com/file.php)
which is saved in the External (private) Storage, but does not require READ_ / WRITE_EXTERNAL_STORAGE permissions.
This app-specific (private) folder can only be accessed by your app.
2.2. Removable (micro) SD card
There may also be another external storage: a removable (micro) SD card
/storage/82C3-E96C/ that can only be read (on modern Android systems / since KitCat).
Note: The root directory of the External Storage
/storage/emulated/0/ is displayed on the device as Internal Storage (unfortunately this is a bit ambiguous).
Here is an excellent overview on this topic: https://www.dev2qa.com/android-read-write-external-storage-file-example/