How to share, upload, download files?

Hi, I’m in the sixth year of my game, an American Football coaching game/simulation, and I’ve added the ability to load any number of leagues, export to csv, and import from csv. However, I’m at a loss on how to let the user actually upload a csv file somewhere where they can edit it, then download it back to the writable area. Once it’s in the writable area, I’m fine, and know how to import it and create leagues.

I’d also like users to be able to share leagues, so that I might put a league somewhere, and users can download it, but again, I don’t know how to upload leagues from mobile devices or download them. I imagine my Windows version will be able to handle all this pretty easily, but I haven’t a clue how to start on iOS and Android.

Any suggestions?

Thanks!