If the text is only for use by the App I agree with Brian Dean. If you need the user to have access directly,. IE Something you can send to someone else Etc. have a look at Erel's B4X Text Editor example.
It provides the means to read/write to external memory. IE SD Card, Gdrive Etc. By pinching the code I have been able transfer files between DirInternal and the SD Card.
That I have been successful shows it is not that hard and Erel has made a great job of keeping it simple.
Regards Roger