App Inventor’s File access component
In the Designer, under Storage, drag the File component to the user interface Design screen. This adds a “non-visible component” at the bottom of the Designer canvas area.
In the Blocks view, scan down the list of blocks until you find File1 (you can rename it to something else). You’ll find a set of functions for writing to files and reading from files.
This component can write text to files and read text from files. If you are familiar with other programming systems and concepts, this type of file and its use are called “sequential files”. Since Comma Separated Values (CSV) files are a formatted version of text files, you can also convert lists into CSV rows and write those to the file, creating text files filled with data that can be read into spreadsheet programs.