How to write/read/rewrite files from a web server using an Android app?

I'm trying to developp an app with friends. I would like to save data on a server after creating something on my app, so that my friends could see what I saved when they launch the app. One more thing is that I would like to be able to rewrite the files. I was thinking about using my Raspberry Pi as a web server. Any idea how I could do that ?

Thanks